Fluid Leaks?

I'm 30 weeks pregnant and I've been having some cramps that feel like menstrual cramps along will lower back pain, I called my doctor and they said as long as they go away and I'm not having any bleeding or fluid I should be fine... I've been having discharge my whole pregnancy that she said was normal but today I have clear liquid in my underwear that doesn't look like my normal discharge. Should I be concerned? How much liquid is enough to have to worry about?