Many things influence mood or cause notable mood shifts, mentrual cycles, thyroid imbalance, general hormonal imbalances too, those come to mind first, but I know there's more.

Bipolar is so much more than mood fluctuations, so if that is your only symptom I would have to say "no", even though I'm no professional.

I would speak to a GP if I were you, and have any and all medical issues ruled out, then take it from there...