I Am 25 Years Old, Got Married 1year Back, From

I am 25 years old, got married 1year back, from last 3 months I am trying to conceive but with no luck .. I am having normal regular periods of 7 days, but yes I get extreme abdominal cramps for the first 2 days of my periods, then slowly it subsides after 36-48 hours (on the 2nd day) .. I take pain killer to control my pain,but still the pain doesn't go away completely it stays and again pain starts badly when the effect of medicine gets over .. Why I am unable to conceive ?
I know the most fertile day for 28days cycle is on the 14th day, so one should start trying from the 11th day till 20th ..
I don't have any health issues, what can be the reason for my infertility ?