If you have your original prescription bottle with your doctor’s name, that should be sufficient.  There are a few prescription drugs that you can’t bring into Mexico and a few non-prescription drugs (like Sudafed) that are off limits.  Best to Google this before your trip as this list is always changing.  Plan to bring enough for your trip or at lease 6 weeks, you can usually source the prescription here in a local pharmacy (some will require prescriptions, but keep trying other pharmacies, one is likely to sell it).  I recommend to start looking for meds you may need as soon as you arrive, don’t wait until you need them.