Could be perimenopause, could be a polyp or a fibroid, could even be a miscarriage but it seems odd it would have happened two months in a row if so. Basically if blood seeps into the uterus and then sits, it forms a clot, and out comes the clot. You should probably run it by your ob-gyn.
My own experience is very similar to what you have described, I am 52 and believe that I have been in perimenopause for years and years and...... I had very erratic periods and could never predict when one would arrive it could be anywhere from 10 days after the last one to about 3 weeks. Sometimes the 'period' was hardly anything more than a bit of spotting, on other occasions I would flood and didn't leave the house as it was so heavy that my clothes would be soaked through. The size of the clots were quite scary too. I had always had clockwork periods prior to peri. My doctor thought this to be unacceptable and referred me to a gynaecologist and I also had a TV and kidney scan. I was found to have fibroids and a thickened endometrium (above average) Apparently fibroids can cause flooding and clots. I was offered a D&C which I chose not to have as I had heard from lots of people that this procedure does not necessarily fix the problem and I believed that I was so near to actual menopause that I would let my body try to sort it out and rebalance itself. Obviously you have to made a judgement based on your own personal circumstances, beliefs and what you are able to cope with. If you have a supportive GP maybe you could discuss the options? My gynae said that tablets were also available to help with the problem if D&C not wanted. I presumed this would be HRT. My periods stopped altogether 1 month after my gynae appointment (8 months ago).
I think it definitely sounds like you are in perimenopause but if there is ANYTHING at point that you are unhappy with or worried about it is always worth getting an opinion from a professional. Take care