I would think it would be picked up on in school, but although that it's very common. Services should be provided for free by the school.
And if he's truly dyslexic, how does he KNOW he sees them "backwards"? It looks diagnosed dyslexics.
If this is a new problem, as you imply, I'd question that and have him evaluated. Not sure why it would suddenly develop if you are sure he knew the difference before. Is he just learning the difference between upper case and lower case letters? Or are they too blurry for him to see the differences? Are you drilling him too much and he's getting frustrated? Start with the in-school services, and mention it to the pediatrician who should be able to administer a very basic eye test at the next visit and tell you whether there's any indication that he should see an eye doctor.