Did he have drug use in his past? If so, drugs can actually cause a male to have a low sperm count, sperm could have malformed shape that causes them not to swim good, but the good news is that there is a prescription to help with that issue. Seek a fertility specialist and they can help u more k. Hope This helps.
The drugs in all honesty probably didn't hurt your chances in getting pregnant. However, you do know that there is only 1 certain time every month you can get pregnant don't you?? If not then your boyfriend may not have been ejaculating inside you on the right days. If you have any questions please just ask.