Infrequent weeing (3 year old daughter)

[goddessofdawn]

My daughter has been toilet-trained for almost 4 months. She is 3 and 2 months old. She used to wee a normal amount - 5 to 6 times a day, but this has cut right down to 2-3 times a day. Most times she is reluctant to sit on the potty or toilet. She does not have accidents - she just doesn't wee very often. Her fluid intake is pretty low - maybe 300-400mls a day, despite me doing my head in trying to increase this.
She can go 8 hours without doing a wee! I try to physically put her on the toilet/potty, and she will kick and scream and physically remove herself.
She does not answer my questions about whether she needs to go. I tell her not to hold in her wee, but have no idea whether she listens.

I can't figure out what the issue is, but I'm guessing it's a combination of stubborness, being "in control", and not wanting to interrupt playing.
When she does finally wee, I watch her carefully and there is no sign of discomfort or pain or anything like that.

She has been awake for 3 hours so far today, and still has not done her "morning wee"! She has had a few sips of milk to drink, but can not be "encouraged" or "forced" to drink any more.

Do I need to take her to see a doctor? Although I'm not sure what they can do. No one can "make" her do anything.

EDIT: Hmm, I just accidentally induced a wee - I made her laugh! And with the laughing, she headed off to the potty.... Hooray.