Hello Doctor, I'm Experiencing Some White Dust On The Top

Hello doctor, i'm experiencing some white dust on the top of my penis. I've been to my village and swimmed there on a lake for several hours continuous and after returning from there this all happened. So for the first week i thought that it must be some salt water effect like itching and redness on that part. But after that i applied some oil and powder so the itching went. But after 4-6 hours this white substance regularly come. I'm sexually active too, so very scared about this. Please advise me and help me out.