bacterial infection
"I'm not sure where these doses of 400mg and 500mg are coming from.  Typically, you would take 150mg, 300mg, 450mg, 600mg, or even 900mg.  Unless you had some weird IV dose, you couldn't possibly take 400 or 500mg capsule form by mouth.  Are you sure you're taking Clindamycin?  I've taken 300mg every 6 hours  without issues, but everyone responds differently to antibiotics."