serious?

For the past few days I've had to pee a lot more than normal like every time I sit down I have the urge to pee and that it's a full bladder but when I go to the bathroom it barely anything and after all the urine is out I have the feeling I'm still peeing but it burns slightly.. does anybody know what could be wrong and if it's serious or not.. I've been drinking nothing but water but I don't drink a lot.. it doesn't make sense to me..