5 or 6 days ago, I slept all through the night wearing only a boxer. the next day, I noticed a slight itchy pain closely at the tip head of my penis. the next day, I saw a dotted blister at same spot where I noticed the slight itchy pain. At first, I thought it was the work of an electric ant, because presently at the area where I live, there are electric ants. so I decided to use antibiotics. But the blister is now spreading, getting to my penis mouth hole. I m scared and worried. What could this be? STD? No painful urination, no serious itching scratch, no serious pains