Possible infertility??????

So I am 24 years old, my husband is 26. I have a 6 year old son from a different guy. Anyway. When I had my son 6 years ago it was a planned C-section and so we were able to put an IUD in during the C-section process. Well it was the Mirena 5 year. So I had it taken out 9-4-13 (it was up) and we haven't used any BC at all since. We are not trying as hard as we could be, but I am just starting to wonder why we haven't gotten pregnant. My husband thinks he could have a problem. He was in the navy for about 3 years and was working on the planes and around chemicals. But we don't know. We don't have the extra money to go and see doctors when we don't know for sure if there is a problem. We did have a positive about 4 months ago (after being 4 days late) but I started my AF later that day. So I just wanted to see what you all say before I try to schedule appointments at clinics for infertility testing. I'm in my fertile week right now and we had sex the day after it started (24th) and as well as last night (which was my most fertile day) and we are going to do it tonight too. What do you all think? And also do any of you have any tips or suggestions for becoming pregnant? My first child was not planned. I just don't want to wait and have an even bigger age gap than we are already going to have. Thanks in advance. And sorry this is so long.