Trying to get Pregnant

Why does it seem that getting pregnant never happens when you want, and by the time you are ready to just go on and forget it it happens. Well, I am still not pregnant, and I have gone from actively trying to get pregnant including ovulation drugs. On through forgetting about it, back to wanting to get pregnat again. Why is that when a woman wants to get pregnant all her friends come up pregnant and every other woman at Wal-Mart is about 3 months pregnant already. It is almost like I am not suppose to get pregnant. Of course though I have to believe that I know better. Oh well, things will happen when it happens.