I do not know.
Yes, it probably could be stress, combined with catching a couple of infections and having to take nasty, stomach-upsetting antibiotics to get rid of them. If that's the case, then maybe a little more time, taking it easy, getting plenty of vitamins, etc might get you better.
But there might be something else going on, too. I would continue following up with the doctor until I got some answers, or started to feel better. Did he have any ideas on why your white blood cells are low.
One thought--white stuff on your tongue could be candida. Could happen to someone who is run-down and taking antibiotics.