Heavy uterus after miscarriage

I miscarried my first pregnancy 4 weeks ago and although I bled for 5 days and passed all of the tissue I needed to I still have a very heavy, achey feeling uterus. I am having pelvic pains and cramps. My symptoms are not heavy but I can feel it all the time, just wondering if this is normal? I should be due for my next period about now but I don't feel like this is a PMS feeling. Thanks in advance