I have been ttc for four years and just started acupuncture about 3 months ago. The acupuncturist says that clots during your period are due to a lack of blood flow to the uterus and can inhibit implantation. You can try baby aspirin and laying on a heating pad on your lower back and abdomen as often as you can! Hope this helps.
Anytime you notice a significant change in your menstrual cycle, its best to run it by your doctor rather than guess about what could be going on.
That's a good question. I have always had smallish clots. But after mc, have had much larger ones. I don't know what caused the change either. If noone here knows the answer, maybe try on the drs forum in the gynocology section. They've been answering pretty quick. Peekawho may know the answer if she's around today.