Gums around last topleft three teeth inflamed on and off for 3 months. last molar became loose and painful; dentist told me clenching caused this. will molar tighten when i get a custom-fit guard? advice on home remedies/practices and what to avoid?

Jaw muscle awareness: A dentist would be able to discuss whether the molar ligaments will tighten over time. To avoid clinching, be mindful of your jaw and mouth position during your daily activities. For example, when driving, working, cooking, etc., hold your mouth slightly open so that your lips do not touch. Tell yourself "mouth open, teeth apart." About chewing gum and ice.

Inflammation: When inflammation is present there is always concern about infection, which would be unusual at your age. If you are clenching/grinding, a custom fit splint should reduce symptoms. If they persist, see a Periodontist.