im a 17 year old male and I am currently concerned about my penis.

I am beginning to become concerned at the fact that my penis does not seem to produce semen. I am becoming concerned about this and currently do not know why this is happening.

I have produced amounts of semen before (not alot) and have gone to the toilet and disposed of it there(only a few times). I think that I may have an issue? Can you tell me how I could test myself to see if its just me doing things wrong rather than my penis?

thanks in advance