How Can I Stop My Gum From Bleeding Excessively? On

How can I stop my gum from bleeding excessively? On Friday it was bleeding for 30 hours.
It finally stopped on Saturday night and started suddenly at 3:30 am on Wednesday morning when I awoke with blood in my mouth. Then it began again at 7:30 this evening. It's now 1:25 am and I can't stop the bleeding. My dentist said he's mystified and offered no help. My doctor was sympathetic and arranged a blood test but I don't know the results yet. He also prescribed antibiotics in case there is an infection. It's coming from behind a Crown I had years ago. I had a filling in the tooth next to it and deep scaling but that was 9 days before the first bleed.