Like Joy said, the only way to know for sure it to have them do a swab and test the liquid. It very well could be urine, however if they test and say it is NOT amniotic fluid but you feel it's NOT urine....I would get a second opinion. The reason I say that is with my oldest son, I was having some moderate contractions and leaking a little....not sure if it was urine or Amniotic fluid i went to L & D. They tested a swab and said no it was probably just urine and sent me home. I got to really paying attention and noticed that it really didn't feel like my bladder letting go a little, which you can usually feel. Especially if I had JUST peed i would get up and immediately get a little wet again... so I called my ob and she said to go BACK to L & D and have them check again. I DID have a small leak, but when they checked that morning my positioning was preventing any leakage therefore they didn't get any on the swab. When I went back that afternoon...I got there just before 4 pm... My son was born at 6:20 pm that evening.
My whole point is if you dont' feel confident, be assertive :)
Like Joy said though, most women do have bladder problems during the 3rd trimester....we'll pray that's what yours is since you aren't quite full term yet.
When in doubt call your doctor. They'll more than likely send you to L&D to test for amniotic fluid.
More than likely it is just urine as your bladder is being smashed pretty flat. Bladder incontinence is a major complaint of the 3rd trimester.