Suggest Remedy For Penis Problem

I'm 24, 6'2" 214lbs. and I'm in good health.Today I noticed that I have a small (~2mm diameter) black bump under the tip of my penis (I'm circumcised if that matters). It is smooth, raised, and round, but cannot be broken by pressure. When I touch/pinch/squeeze it I feel sensation in it similar to the surrounding skin. I've never had sores on the skin of my penis so I don't know if it would feel more sensitive than the rest of it if it were a blister.The only thing I've been able to come up with that looks anything like it is a blood blister, but it seems extremely small to be one. I had typical-for-us sex with my girlfriend last night, and nothing seemed to hurt. We're both clean, and I've not done anything silly like get caught in my zipper. As far as I know this was not here last night.Does a blood blister sound fitting or should I consult a doctor about this?