Miscarried but hcg still rising

Hi! I found out I was pregnant two weeks ago. They had me come in last Monday and last Wednesday for hcg test. Monday it was 55 and Wednesday it was 68. She told me I was going to miscarry and wanted me to come in yesterday for an ultrasound and a blood test. They didn’t see anything in the ultrasound but my hcg went up to 72. I started bleeding on Sunday and passed a small clot yesterday morning. Has this happened to anyone? They’re having me come back in tomorrow for another blood test.