This is a very common symptom of pregnancy especially in the first trimester and can happen as early as one week after conception. As the progesterone level rises and the embryo starts to produce HCG, blood supply to your pelvis increases and this causes pelvic congestion. Your uterus takes up more space now, thereby putting pressure on your organs, your bladder included. The bladder becomes irritable and tries to expel the smallest quantity of urine; this is one reason why most women frequent the washroom only to pee in very small quantities. Congestion is worsened by the extra blood vessels and blood flow developing in the pelvis because of the placenta. All this changes in the second trimester only to return in the third trimester when there is serious space shortage. To deal with this problem, don't try to cut back on your water intake; however you can drink more in the day time and lessen in the evenings to reduce the number of trips to the toilet.
But what if it hurts to pee..
There is reason to be concerned if you get a burning or stinging feeling when you pee a lot; bring this to your doctor's attention. You may have a bladder infection or UTI which needs treatment with antibiotics. If left untreated, it can trigger premature labor. In the meantime drinking cranberry juice provides relief.
Handy Bathroom tip you can use..
Empty your bladder totally each time you visit the washroom. If you think you have finished, sit still for a second and try to go again.