Masturbation question?

well this has been happening for maybe 6 months now... I'm 15, have some pubic hair (Very fine and I'm blonde), can't really see any underarm hair. Anyway, everytime I (I know it's because my glans becomes really sensitive and I just somehow have a way of telling it's climax) no semen comes out... Not even clear liquid? I've gotten hit in the testicular area a couple times, none to make me go to the hospital or anything, but are my not producing sperm? Or am i just too early in puberty to tell? I'm 5'4'' and 150lbs (It seems like I'm overweight, but I don't look like it. Muscle m?) Anyway, thanks for the answers.