I need help on which of three antibiotics to give my seven year old baby boy Rufus that weighs about 1.5 lbs. he has an abscess in his mouth where he broke his top teeth out. I have 500mg amoxicillin capsules, 500mg flaygl tablets , and 500mg cephalexin capsules. I think I spelled those correctly, my apologies for any spelling errors with the antibiotic names.