Trying to conceive

Hi everyone. My husband and I have been together for 4 years now and we have a six year old little girl. He is her father but not her S.D. I had my daughter as a junior going in to my senior year of high school. After having my daughter I ended up having a prolapsed uterus and had to have emergency surgery. Well then my mom decided to put me on depo me being 17 she pretty much had all the say when it came to me...I stayed on depo for 2 1/2 years. I made my way across the stage and into life with the help of my parents and family. Until I met my husband and we have made it through life together raising a child at 22 & 23. Now we are wanting to have More children and we've been trying for 2 years now and nothing. I have gone to doctors they all tell me the same thing Patience is always the key. Any advice?