I'm on my fourth day of taking 10mg Prozac and I've noticed that I've had headaches. Yesterday it wasn't that bad, and I gave it little notice even, but today it's gotten a little worse. I took it about an hour or two ago before I started developing the headache.
As for the jaw clenching, I think that actually may be due to anxiety, but not 100% sure. Same goes for the nausea probably. Not sure.
I've taken Prozac in the past for about a month (where it worked wonderfully for me) before (stupidly) stopping it abruptly before something happened which triggered the depression to come back.
Hopefully these are just normal beginning/starting-up side effects but I don't remember expierencing them the first time I took the medication, so I'm just a bit concerned/curious.