tips on getting pregnant

I really want to get pregnant and my boyfriend and I have tried but it's not working. I've tracked my periods to see if we could time it , but nothing has happened yet. Are there any tips for conceiving? 
Edit: we had sex the first and second day (multiple times) of my fertile period, but it only said there's a 9% chance of getting pregnant. We haven't been able to have sex again, but Will having sex again increase the chance? My fertile window ends Sunday