What's wrong?!

J
We've been ttc for about almost 2 years. No children in our relationship. 
​But my man has a daughter from an earlier relationship. 
​Been to the doc and done test and everything  and  they say that we are healthy and nothing's wrong. But why can't i conceive!? We have sex pretty much everyday. I lay a pillow under my back like the old school way.  
​We don't drink or use drugs. 
​This is killing me!! 
​Every month I get "preggers feeling" with all the symptoms and then period comes on the clock. 
​This is tearing our relationship cuz I feel so useless as a woman.
​Now I'm going to try to loose a lot of weight just in case. 
​Please God. Grant us our wish and bless us with a little heart.