Five days ago I was up all night with severe back pain with nausea and vomiting. In the morning after hours I took some Motrin and was finally managed to go to sleep. Since then I've been having more manageable pain (still hurts considerably at times) in the area with on and off bouts of nausea (no more throwing up thankfully). I wake up constantly during the night and have to adjust my position despite lying flat on my back with one pillow in under the lumbar area. I have been taking NSAIDs the whole time. I don't know if it ties to this but my period is around 2 weeks overdue. I'm 23 years old, I weight around 125 lb so it's not an issue with weight and I'm sure I'm not pregnant (it's impossible). Does anybody have any idea what it might be? Has anybody experienced this? Maybe any recommendations about medicine or what I can do? Thanks.

Many here know that I am not always quick to say 'see a doctor,' but SEE A DOCTOR or walk in clinic!
There are too many possible reasons for what you are experiencing, some not so serious, some more serious. But why stay in this much pain? Plus, even OTC pain relievers have their downside. So go.

Pain and vomiting go with so many conditions, 2 common ones being appendix and gall bladder. Pain isn't always in the spot those organs are located (both are on the right, but pretty far apart, although lumbar pain not likely to mean gall bladder). Your period could be on hold as your body says 'I need to deal with this other thing.'

But it could be related, if you have an ovarian cyst that twists or ruptures.

To diagnose any of those would require testing equipment such as ultrasound, so a clinic is better than a private doctor.

(There's also PID, PCOS, or fibroids, although they wouldn't usually be so dramatic and sudden, and with vomiting.)

So GO! If you have a thermometer and have a fever, go to an ER.
If you aren't familiar with what's around you, use the phone book. Many hospitals have associated clinics, some next door, some not.
And it's Saturday, so do this today.