I know how frustrating it is when you are trying to conceive! We are told (perhaps even scared) into believing that the second we are off birth control....watch out! You will become pregnant!
In reality, though, it is actually difficult to become pregnant, with only a 20% chance of conceiving every cycle! We aren't told this, of course, during our youth (for obvious reasons).
It takes MOST couples 6-12 months to conceive. I remember how excruciating it is to TTC, just to have your period begin. Hang in there, though....you have only been trying for 3 months, and you may need to try for another 3-6 months (or, 12 months total).
How often to have sex? Experts say "as often as possible throughout your cycle". Your most fertile time is usually mid-cycle (about 2 weeks before your period begins), and having sex every-other day or three times a week during your most fertile window is ideal.
If you want to know more about your body, you can use an ovulation predictor kit, take your basal body temperature every morning, or use other tracking methods to know when you are most fertile (please note: these are not exact measurements, hence the word "predictor").
You can read this article for more emotional support: Emotional process of TTC.
We also have a TTC Group, if you would like to talk with other women: TTC Group.
Lastly, just use the search term "trying to conceive" at the top of the EmpowHER page, and you will find hundreds of discussions and articles related to this topic, as well as helpful advice and tips.