Frustrated

I have not planned any of my children and all happened to come about 2 years apart...sadly I lost the 3 child at 16 weeks and its has been 2 years since this has happened and nothing. I'm frustrated and mad and hurt, I want to have another child and am beginning to worry if I can anymore since it hasn't happened. The doctor assured me everything was normal after my miscarriage but the continued fails when there is no protection being used is disheartening me....please help, I don't want to give up but I fear I may be starting to.