Pregnancy is a finicky thing, it could be her first time, her one hundredth or her five hundredth time when it happens. For me I've been sexually active for 5 years, used little to no protection and didn't get pregnant until I intentionally tried for 8-12 months.
You have to see a doc for this sort of thing, But seeing as you are pretty young, so far, you have probably just been lucky.
Why the hell are you intentionally trying to knock girls up? Surely you're not independent or successful enough to support yourself, let alone a family!
Anyway, a trip to the doctor and a few of your swimmers under a microscope is the only way to know for sure.
You would have to give a sperm sample to a fertility doctor or clinic, so they could examine it under a microscope.
Might be a good thing because you are terminally stupid and should not reproduce.
Go to a fertility specialist. Be prepared to jerk off into a jar. (If they are close by, you can do that at home and bring a jar in). They will give you a sperm count and a motility level-which indicates their health.
sounds like you are but the only way to know for surfe is to go to the doctor... maybe donating at a sperm bank would give you the required info at a cheaper price because I'm sure they do some kind of test to make sure your not shooting blanks