Welcome tigger, lovely that you had a baby after 15 years of infertility. As for the change in your periods, an acupuncturist would say there's some "stagnation" if there are clots. Can you go to acupuncture? I think it works wonders. I had painful clotty AF, but acupuncture sorted it out for me.
Pink, you have my sympathy, love, I'm in exactly the same boat, and yes it doesn't get any easier. I have been ttc for such a long time, you'd think I'd get used to it, but I haven't at all. It is still a blow when I get my hopes up and still there's a bfn. If women got pregnant through commitment and perseverance, I'd definitely be pregnant by now. If it was because they were deserving, having been through heartache after heartache, then there would be hundreds of women who wouldn't be on mumsnet trying so hard to have a baby. But we both know that isn't the case. I have been on the 40+ ttc threads on mumsnet since 2009, and I am still here, having watched hundreds of different women join this thread, get pregnant and leave. I really thought I would be one of them by now.
But like jass says, what can we do but keep on trying?If we stop there will be no chance at all. However, it's perfectly normal to feel completely sick of it all. I know I do. 
On a brighter note, I am a lucky mummy to have had my DS in 2008, at age 41 and 3/4. Yesterday we visited with friends, and he ran around with their two year old who was born just after my first miscarriage, seeing them run around together made me sad that DS didn't get his little sibling, who would be close to that age, and a wonderful playmate for DS.
Jass, you said something about sensitivities caused by having sons. I found that interesting, as both my miscarriages that they did tests on found I had sons. The first miscarriage was due to a chromosomal abnormality, but the next one (though they botched the tests the first time, when repeated) showed no abnormality. Then I miscarried a third time at 5-6 weeks - my tests never really got dark, and I wonder if maybe I have a sensitivity too. I had some blood tests which suggested an autoimmune condition may be imminent (but not present yet), which had me thinking that maybe I was rejecting the fetuses. My doctor is not convinced. She was prepared to put me on progesterone if I get a bfp, but thinks the miscarriages are age-related.
This is all conjecture as I can't even seem to get pregnant anymore. I have had 9 pregnancies (five THBs) in total, but now that I am past 45, I can't seem to do it again. It's been a year since my last bfp, I wonder if I will ever see one again?