What could be the causes of burning sensation while urination?

I am 27 years old and since last few days I have been having a burning like sensation while urinating. I have a girlfriend and I have had a few encounters of intercourse with her. Could this be due to some sexually transmitted diseases that I am facing this burning sensation? I want people to educate me on the possible causes of this burning sensation while urinating. Can you please suggest an effective treatment? Thanks!