Overactive bladder?

[Q2C4]

We started potty training DD a month ago. She is nearly 4. We waited ages for her to show signs of wanting to potty train but she never did so we eventually just took the nappies away and we're following the Oh Crap method. DD isn't constipated but she was last year and is still on 1/2 a movicol a day. Poos are fine - all poos are on the potty or toilet and have been for ages now (pre Jan). However, wees are a problem. She does loads of tiny wees - if she has a drink she will do a tiny wee every 10 mins or so. I measured them and she's passing about 30mls. The largest she ever manages is about 75ml. She has never been dry overnight. She has a lot of accidents during the day if she's out of the house. She does such frequent wees that sometimes she doesn't get off in between.
My question is, is this normal given we're only month in, or is this indicative of an overactive bladder, and if so, should I take her to the GP?
Thanks