Sore throat with white gunk on my tonsils. Strep neg. Got a rocephin (ceftriaxone) shot and have been on ceflex for 4 days. Now have red spots on roof of mouth! Help?

Pharyngitis. Difficult to understand why you were given a Rocephin (ceftriaxone) shot and placed on Keflex when your strep test was negative. One can have a horrendous looking throat due to just a viral infection, mononucleosis being the most notorious. If pain is improving, then consider waiting a bit longer as it may all sort itself out. Otherwise do follow-up with your doctor now to be re-evaluated.
Viral. May be viral and antibiotics won't help. May need a mono test.