Ent specialist- prescription cephelexin 500mg 3 /day - tonsillitis. urologist- prescription sulfameth/trimethoprim 800/160 2/day for cultured uti. can/should i take both?

Yes: Yes, you should take both. Different antibiotics are effective for different kinds of infections. Unfortunately neither antibiotic you have been given would treat both tonsillitis and UTI very well. So i suggest taking both as prescribed, along with a daily dose of probiotics from your local health food store to prevent a yeast infection and keep your normal internal bacterial flora in balance.