I am on phentermine and cannot sleep due to the numerous bug bites I have. I took one Benadryl (diphenhydramine) allergy. Anything I need to watch using both these meds?

Drug to drug. Increased drying of mucus glands in eyes, nose , throat may occur. Internal eye pressure may increase and you may experience difficulty with urination or constipation.
Minimal concerns. Usually if anything Phentermine will keep you from sleeping. Benadryl (diphenhydramine) is sedating. This should be fine. I am not concerned! Hope you can get a good night's rest!