The pharmacist told me I could drink in moderation with the generic bactrim (sulfamethoxazole and trimethoprim). I did that two nights ago. Could it cause any harmful effects now?

Not now. The pharmacist may be correct, but it is always risky to mix alcohol and medications.
Bactrim/Alcohol. Typically mixing alcohol with most drugs can be dangerous. You should always ask your pharmacist about the complications of your medications mixed with alcohol and other drugs. Mixing alcohol and Bactrim (sulfamethoxazole and trimethoprim) has been linked to flushing, heart palpitations, and headaches from the build up of the toxin acetaldehyde. You should minimize your alcohol consumption and notify your physician of problems.