Weird penis behaviour, don't know how to explain better.

Hi,

I've just turned 16 and have some concerns about my penis. The problem has been there for the past 6-8 months I'd say, perhaps longer.

This is the issue. For much of the time, my penis shrinks to about 2.5"s long. The bottom half of the shaft is swollen, while the top is very shrivelled and wrinkly. The transition between is very sudden. When I go to urinate and find it in this state, I can't freely urinate, instead I must let it out very slowly, as doing otherwise causes considerable pain, and the urine does not flow out. When it is like this, my scrotum is also very tight and contracted, not painfully so, I just thought this might be important. I think there's some sort of blockage as pulling apart the hole at the top of the foreskin instantly allows the urine to flow. 

I think I have either Frenulum breve or phimosis, as when I masturbate the foreskin can't be pulled past the head. 

I'd really appreciate any help, as I don' t feel confident enough to urinate at urinals now, because of how embarassing it would be.

Thanks.