Fertility Testing

I'm posting this in Birth Control because I want to test my fertility to know my chances of accidentally getting pregnant. The only birth control method I use is withdrawal, and I've been pretty lucky so far. I don't want to keep pushing that luck though. I want to test my fertility because I think I might be infertile due to hormanal imbalances and several chronic illnesses. What is the best way to go about this? I don't have hundreds of dollars to spend on doctor visits either. Are there reliable at home tests? Thanks in advance!