Dana is exactly right. All pilots have to assess their fitness to fly before each and every flight. If you're having a rough day and you don't feel that flying is a safe activity today, then don't fly. If your doctor put you on a new medication, wait a week or two before you fly again to see if there are any side-effects. As long as you're responsible about making an honest assessment of yourself, your doctor is aware that you fly and hasn't advised against it, and none of your medications carry an advisory against operating motor vehicles or machinery, you should be fine.
Oh, and I'm not a lawyer.
If you have specific questions, my advice would be to join AOPA, then call them and ask to speak to an aeromedical advisor. Details here:
https://aopa.org/go-fly/medical-resources