If it's an infection, the antibiotics may take a couple of days to clear it. Is she drinking okay, and are the piglets still feeding regularly?
I can't remember how old you said the litter was, but guessing a week or two by now. Get them started on creep food asap and maybe try and get them lapping from a shallow dish - just in case the worst happens and you lose the sow. I really don't want to worry you, but this is what I would be doing if I wasn't sure how things were going to turn out with one of mine.
Fingers crossed that whatever is causing her to be under the weather clears soon, but put your plan B in place, just in case.
Good luck
Liz