What Causes Dry And Tight Foreskin And Yellow Discharge From Penis?

Hi there, I'm an 18 year old male and I seem to have a case of dry and tight foreskin. About a month ago I could easily retract the foreskin with ease but now I find it very painful. A yellow discharge seems to be coming from underneath also. I was wondering could this be the result of the anti-biotics I'm taking for my pimples. The anti-biotics are called 'by-mycin'. Any help would be great on why this is happening and how I could treat it.
Thank you.