What could be wrong with my husband? What kind of learning disability could he have? Am I being to harsh or do I have reason for concern?

This is a big problem. 

You say he is not very smart. He has probably heard that his whole life amd that is why you are seeing anger when you bring it up. 

He needs to be tested by a professional for learning disabilities.  He may find out a way to learn and work around his problems.  Sounds like they just pushed him through school without seeking out what his problems were. Or assuming he was “dumb”.  

My son has learning disabilities. Many have nothing to do with intelligence. He is very smart and insightful. 

It may not be a LD. You don’t know. He doesn’t know, which is why is must be brought up to a doctor and addressed with the right professionals and tests.  

Do,you do things for him?  Do you cover for him?  Perhaps let it go and let him see how much he can not deal with every day tasks.  

It's possible he merely has a left/right brain disorder. A good friend of mine, who lives alone and manages by herself, is a great conversationalist, cooks great food and is an excellent amateur artist and embroiderer, but has no educational qualifications whatever, and can't handle figures.

I have to help her write cheques, and the last time I told her to write "2021" in the date box, she wrote "20" and then "20" again, and then "1"  - 20201.She can't tell what the decimal point means and gets in a panic with her bank statements because she thinks they're telling her she's got 600 pounds in her account rather than (in fact) 6,000.

But there is nothing actually wrong with her. And I suspect your husband may be the same. Step back for a while and don't comment or criticise. Some of it may be a feeling of being under pressure from you.

Worry about wrong dosages if and when the situation arises. Don't surround him with "What if?s" Let him be; watch, observe, and don't be so quick with your complaints.

A separate question, but one that I'd love to know the answer to, is How on earth did you manage to be around him long enough to know you wanted to marry him, without noticing any of this?

My son's father is intellectually disabled and I didn't catch it...his cousin told me when my now ex and I had been together for a while.  His mother trained him well enough and he learned a lot of social skills on his own.  He was in special education and hadn't ever taken a proper English class so he had very poor grammar and English.   The one thing you can do is accept him for who he is because you are his wife not his teacher.  My son is intellectually disabled and has not learned much academia in his 30 years.  I try to teach him and he says he already graduated.  He learned to read when he was eight years old I taught him myself because the school said the best thing for him to do is play.  I bought him hooked on math but he doesn't want anyone to know about it.  I bought a for him almost

Your husband is almost totally illiterate. When did he quit school? He must have been young when that happened. That's why he is the way he is. He's not stupid, he's not learning disabled, he's just IGNORANT because he either never learned anything constructive or was never taught anything when he was growing up. Or perhaps it's both.

There are ways around this, but they require hard work and commitment on your husband's part. He CAN attend adult literacy classes- most public libraries generally offer these at little or no cost. Some of them also offer remedial education in math, too.

It's possible that your husband might have dyslexia. That might explain his tendency to reverse figures and read words backwards. I'm also not surprised to hear that he gets defensive when you try to talk about his limitations. Being illiterate is EMBARRASSING for most people, ma'am. No one wants to admit that he or she can't read, write, or do basic math, because our society is one that treats people badly because of it. You're correct that he shouldn't be permitted to do certain things, such as give your children their medicines, for their safety. But there are ways to handle this tactfully, such as by volunteering to do it so that he doesn't have to worry about it.

i would ask him about it

the are multiple possible problems.  dyslexia was only recently discovered to be a hearing problem that, afaik, remains uncorrectable.  when multiple letter sounds are similar or identical to the person with dyslexia, they frequently fail to learn to read ... [the sound difference between 'bead' and 'deed' and 'peed' isn't detectable -- so the usual method of learning to read -- associating letters to sounds -- doesn't work and letters/spelling seem totally arbitrary].  since your husband is an adult now, there likely is no one other than his physician who might be able to get him to accept being tested.  dyslexia is not the only possible condition that might cause something like this ... it's just the one I happen to know a small amount about.  -- grampa