I Am A 19-year-old Male. After Having Sex Two Nights

I am a 19-year-old male. After having sex two nights ago, I had a mild stinging sensation while urinating the next morning. I've had this stinging sensation ever since and it is worse today than it was last night. My stream is weak and is going every which way, as if part of the end of my urethra is blocked off or something. What should I do?