35w3d - Contractions 20mins apart - Help?

Hello everyone. I am a first time Mom and for the past two hours I have had regular contractions about 18-25minutes apart...

I am used to the Braxton Hicks, but these feel like stronger menstrual cramping and I am getting worried. I lost my mucus plug, or at least part of it, on Sunday morning.

I'm not really sure what to do, if anything. I have been trying to relax and I have been drinking plenty of water all day.

Has this happened to anyone else? Advice? If it continues I will call my doctor, of course. But, I know theyre short staffed this week and I dont want to bother them over nothing.