Just a suggestion: It's possible you're allergic or have a food sensitivity /intolerance to it. I know a lot of doctors say you can't be allergic to vitamin c, but there are people out there who get allergy-like reactions to it. You can simply google "allergy to vitamin c" and see a lot of people having problems. It may not be the c itself, but elements of what makes up the supplement. My sister has a genuine allergy to oranges, but I don't know if she has a problem with c supplements. I guess if you were willing to experiment on yourself, pick a day or few, and eat lots of oranges, and only oranges, and see if you get the same result of swollen gums as when you take the vitamin c supplements.