Go see your doctor!!!!!!!!!!
Its really swollen, I got a huge knot on my elbow
If you don't see any bruising then It could possibly be tennis elbow. I had elbow pain after loading our rv for a trip. It would throb and finally got so bad I had to go to see my primary care doctor and she gave me a cortisone shot. She also told me to try icing it. If the pain gets to bad go and see your primary care physician.
You could have banged it while sleeping. hitting it hard enough, and hurting it badly should have woken you up at the time it happened though. Being pregnant may be a factor in why you didn't wake up, but I'm really not sure. Try putting ice on it for 20 minutes and then off for 20 minutes. This can be repeated for the first 24 hours, then it's not going to be effective. I'm not sure what you can take for pain, whether or not even tylenol is safe, since your pregnant. Call your doctor or pharmacist and ask them. Ask them about your elbow while your at it. The doctor might know some things to ask in order to rule out certain things.
Good Luck,
sean