If I am having cramps does that mean I am probably not pregnant?

I have been having cramps off and on today I am supose to start my period Monday or Tuesday, but at the same time we have been trying to consieve. I have not had any luck yet and we been trying since the beginning of September. With my first I got on birth control then 2 months later got off of it because I deiced we wanted a baby. My second baby I wasn't on birth control, but we decided we wanted another and it took us a month to get pregnant with that one. I have been trying almost 3 months now and no luck. We have intercourse every other day - every 2 days. I lay in bed with my hips elivated and I lay there for at leat a half hour to an hour before getting up. Why am I not getting pregnant? My periods are anywhere to every 21- every 31 days, but mostly being nomore than 29 days. I am 28 years old. I am pretty healthy so I am not sure why I am not getting pregnant. But I don't want another baby so clothes to christmas since DH is a month before christmas then it is christmas and then 2 weeks and 3 days later is our youngest dd's birthday. So I have one more month to try to consieve and if I don't by that month I am going to stop for a while so that I don't get pregnant so close to christmas.