My front teeth have been feeling loose and sore since i purchase a boil and shape mouth guard. what do i do?

Stop using it..: ... and see a dentist for a professionally fabricated and fitted appliance. You are damaging your bony support by having this appliance move your teeth back and forth.

Stop wearing it: While they are useful for diagnostics and some issues, these OTC mouth guards sometimes are the wrong solution for a fairly complex problem. Given your observations, stop wearing it and take it with you to a dentist for a thorough exam to properly diagnose what is going on with your bite. A custom made splint or modification to the one you have may be indicated.

Made wrong: The retainer was made wrong, causing some destabilization of your front teeth. It's working like an Invisalign tray. See your Denistry for 1) adjustment, or 2) fabrication of a custom mouth guard. Unfortunately this seems to be one of those, "you get what you pay for" scenarios.

Dentist fabricated: Do not use any nightguard or mouthguard that is stock. Stay away from any make it yourself trays. If the tray does not fit, stop wearing immediately and see your dentist to have a custom fit made.

Do not wear it: Toss it in the trash. See your Dentist for a custom made mouthguard made on the cast of your teeth. If it is a sports soft flexible guard, then it should not be too costly. Explain the situation and purpose to the Dentist and, if for sports, they may give you a special fee, as you are exercising preventive safety measures. Good Luck.

Discontinue ASAP: If you continue to have pain after more than a week or so discontinue immediately, You should see your dentist as soon as possible for evaluation, diagnosis and treatment.