I took my last bactrim (sulfamethoxazole and trimethoprim) ds at 7 am. can i have a couple of beer's tonight or no?

No problem: Alcohol in moderation doesn't interfere with most antibiotics and doesn't have any effect on infections. You dould have had "a couple of beers" any time during your course of treatment, and certainly can do so now. Of course heavy alcohol can interfere with the immune system's ability to fight infections, so don't overdo it.

Alcohol and meds: If you are done with your medication you should be ok to have an alcoholic beverage. However it is always a good idea to run this by your physician or pharmacist because there may be underlying circumstances that only they would know about!