I had a weak erection once with my gf, i am 25, no std, penis burns urinating, thick liquid comes whn deficate, and while little excitement, am i n trouble?

Need more info: Some of what you describe is unclear. Are you having white discharge from your penis? If so you need to see a doctor asap and have yourself diagnosed and treated for what may be a std with urethritis. Every man has experienced an occasion in which they were unable to get a full erection, and unless this becomes a regular occurrence would not worry. Good luck.

UTI: You may have a urinary tract infection and prostatitis for which you will need antibiotics and should see a doctor.