M.H.
Well Nine out of 10 people. Your most fertile days are about 11 to 16 after the beginning of your period. The the 13-15 day is your main days but you have a higher % on the 11 - 16th days and remember it takes up to 3 days after you have sex for you actually to conceive. That is why you have to basiclly have to wait a month from beginning or your period to the next period to find out if you are pregnant. b/c you have to give your hormones time to elevate a little b/4 a pregnancy test can tell in all honesty. When you take your test and its positive you really aren't but like 10 days pregnant. But people say a month along b/c you go from your last period. Like when you are 3 months along your baby is only 2 1/2 months.
Now I am 4 months pregnant right now with my 2 child and I knew a week before I found out b/c I had a little nausea but not everybody has that symptom. My breast got sore pretty fast too. Take a pregnancy test the day you are suppose to start your next cycle and you should be able to tell.
Good luck! I hope this helps.