Should I go to the doctor?

I'm 18 weeks and 4 days pregnant and I've been having, what I would say are bad, cramps since I woke up (at like 9am. it's 4pm now) and I've been super nauseous all day as well but I didn't actually vomit until a couple minutes ago. Before I puked, I was really lightheaded, short of breath, and my heart was beating really hard. 
I'm not running a fever but I keep going from like sweating to freezing. 
Naturally, I'm worried but I don't know if I'm being overly dramatic. 
**EDIT: because it's Sunday I couldn't call my doctor, but I called labor and delivery and spoke to a nurse. She told me to rest and stay hydrated, but this was about an hour and a half ago and I was only having cramps and feeling nauseous.