Well, I can tell you the things that I've had so far and what the docs have told me in case it sheds some light on something you haven't thought of yet. I've been ttc for 23 months. I started seeing an RE after 6 months because infertility in my family is unheard of. They ran all the blood tests on me and a HSG to check tubes and SA and some limited blood test for my husband. HSG came back fine, but RE said one tube might be kinked down a little with an adhesion but it was open and was probably fine. So he told me to try for 6 more months. I came back at 12 months ttc and we decided to do a LAP and dye; which wasn't so bad: I was more messed up from the anesthesia and the pain in my shoulder from the gas they inflate you with (don't worry Sophe its really not that bad, and worth it to find out if anything is wrong). They found mild endometriosis (they cleaned that) and released the one tube. I was then told to come back in another 3-6 months if still not prego to start IUI, but he never really explained why he thought that IUI would work. I was ovulating every month so it made no sense to me, I felt like a flow chart and I never went back to that RE. (Also, we always used an LH test to make sure we were timing things correctly)
Then at 22 months ttc I finally got in to see my new RE after a 2 month wait. This RE suspected that the reason I wasn't getting prego was that I have PCOS. This came as a huge shock and I never considered it because I'm very thin, I don't have excess hair, I ovulate every month...I had no symptoms of PCOS. As it turns out I don't have PCOS (my testosterone levels are fine) but through ultrasound viewing I do actually have polycystic ovaries (I had the string of pearls along the outside of each ovary). The RE told me that due to the PCO I was most likely not producing good quality eggs. So now I'm on my first clomid cycle. I have to take clomid from day 3-7, then on day 16 or so they do a post coidal test to see if the clomid dried me up or not (luckily this month it didn't so I got to save $500-$1000, yay), if it does then I have to do an IUI; then trigger shot, then 4 days after trigger shot I have to take vaginal progesterone until the preg test. Right now I'm in the 2ww, so I'm feeling rather anxious. I have to go on Thursday to the RE for the test.