I've experienced both things, antibiotic and new med, recently myself but at different times. I was taking an antibiotic a couple of months ago that made me really depressed. I stopped taking it after a week because I couldn't stand it any longer.

Then, just a few days ago I started on a new anti-depressant. I started out with 12.5mg and the goal is to reach 100mg. With the first dose of 12.5mg, I was a little more tearful than usual. Twelve hours later I took the second dose, and this time I was ok. Three doses later, when I went up to 25mg, I was very tearful and sad, so I decided to go back down to 12.5 for the next dose and felt pretty good. This is where I'm at now. I plan to stay at 12.5 for at least another two doses before I try 25mg again.

I don't know if you've gotten a hold of your doctor or figured out your antibiotic or not; but, if you start Sertraline again, you may want to begin with a lower dosage, like cut the 12.5 in half or even less for a few days. Starting out with half of the ultimate dosage can be quite over-whelming. I'm being started out with only 1/8 of my ultimate dosage goal.