@Carly1306 is right it took us longer than a year actually to get prego. I was on time with my periods too but I found out that I get them but didn't ovulate at all. so my OB gave me clomid. Just relax even though its hard as &^%(% to do so especially if you want one so bad like me an my hubby.
My son is now 5 :) hang in there sending you baby dust!
4 months is no time at all to be trying to conceive. It takes a normal healthy couple at least a year to conceive naturally.
All you can do is track your cycles, and time sex for every other day leading up to when you ovulate, and then again for a couple of days after.
After a year, if you have been unsuccessful, then the doctor will be able to look into things further.