So a week before my last period i had a little bit of bladder leakage daily/never happened b4im a healthy weight, 26 hrs old/ am not a mother, but for years i only drink coffee daily am dehydrated regularly, is this oab, can it come that suddenly?

I feel the incontinence caused by overactive bladder is accompanied by the urge to urinate& frequency., Caffeine may be playing a role in your case without the urge. Bladder leakage without the urge is usually caused by weakness of the pelvic floor from previous childbirth which is not the case with you but perhaps hormonal changes around period time causes bladder outlet weakness. See urologist

No it is not OAB. It might be a one time occurrence. Drink water, avoid constipation, do not hold urine when you have to go and you should be OK