BinB,
Although he's very young, and his teachers are correct - he's still within the wide age range where this type of challenge can be very typical - this is a red flag:
He started kindergarten this fall, and so far it has been very stressful for him (and the whole family) -- he comes home exhausted, grumpy and oversensitive and has been acting quite aggressively, which is unusual for him. He is not at all excited to go to school and has a hard time completing his school work and homework.
Most neurotypical kids who are developmentally on track, whether or not they are still reversing letters or not recognizing phonics etc at this age - aren't coming home from kindergarten stressed out and exhausted.
I am a firm believer (as the mom of two children with LDs) that listening to your mom's intuition is really important - if you think there might be a problem, and you're seeing signs like this, it's most likely worth pursuing an eval. I would start by asking your ped what he/she recommends, who in your area etc.
Is there any way to test a child this young? And if he is dyslexic, what can be done to help him cope? I hate to see him falling behind his peers and losing his confidence.
There are so many different things that can be done and so much of it depends on the individual child. If you were to find out through an eval that your ds is dyslexic, I can tell you that probably the most helpful thing ever for my dysgraphic ds and dyslexic dd was to give them a *name* that explained what was causing so much frustration for them, to let them know about other famous and successful people who had shared the same struggle, and letting them know that someday it would all be ok - they would get through the struggle of early learning and fitting in at school. BUT - you don't have a diagnosis or know that this is an issue yet. So for now, until you know more, I'd do two things - first I wouldn't make him work to exhaustion and through frustration at home, it's kindergarten. If he doesn't do his homework the world is not going to stop. I'd ask lots of questions of his teachers about his work, what he's doing, where do they see challenges etc. I'd reassure your ds that you care, that you will listen, that you are doing what you can to help him not be frustrated. And I'd get an evaluation

Best wishes,
polarbear