Well I've had retained products, my bleeding after the birth had pretty much stopped when I was discharged two days later but then at day 16 I started bleeding again - sort of like a period but I knew it was much too early for that. Was bleeding on and off for 2 weeks more when I passed a clot. Not huge but certainly the biggest I had ever passed. That was it, no more clots and it all seemed to stop. But then I started getting cramping pains, like a period was coming. Over several days the pains became more like contraction type pain. Turns out I did have retained products and the bleeding ha slowed as a clot became stuck in my cervix. It was too big too come through on it's own and my body was trying it's best to ease it out. I had an internal and the doctor managed to remove the clot stuck in my cervix and could see there was a whole lot more to come as my cervix was still open. It was horrendously painful!! That night the heavy bleeding started, he had obviously cleared enough for the bleeding to come. I was rushed back into hosp as it was quite heavy. Scan showed lots of solid blood clots, possibly placenta but they couldn't be sure. I managed to pass most of it on my own later that evening in hosp but they gave me Misoprostal to help things along. I had two vaginal tablets and one oral later on.
I expected to be in agony when i passed it all but I wasn't - probably due to all the pain relief I'd taken earlier on!
Had a scan the next day and there is just fluid now so they think I just need a big period and I should be back to normal again!
I would say if your concerned def get it checked out, I didn't think for one minute after 4 weeks I could still have retained products as I seemed ok. I must say though one of my main symptoms is exhaustion. I'm so tired, even after sleep!