PLEASE LADIES WHICH ONE HELP YOU GET PREGNANT ON THE FIRST TRY.

I am using Prenatal Mutli + DHA I think I have problems with fertility? I think. I am 21 I have a 1 year old son so something has to be working down there. I got off depo in March (only had 1 shot, was supposed to go back for my second shot on March 6th, never went, got my period march 16th) Period have been regular since, and on time, I have been ovulating I know because this cycle I did opk. I just need help of why am I still not getting pregnant. I have a doctors appt on Thursday. This month is the month that my husband and have actually tried to get pregnant.