What's going on?

So for about two days now I have been able to feel this pulsating or throbbing in my uterus or cervix area it's not the opening of the vagina but not like the Fallopian tube either. Online everyone says it's the baby hiccuping. But I'm not pregnant. Other places say it's early sign of pregnancy but I start my period in 4 days... I had a period last month. The throb isn't painful or pleasurable just there and annoying. Throbs for like 10 pulses then stops for about 5 minutes and does it again! Twos days straight hard to fall asleep and heating packs or cold showers aren't helping. Any suggestions?!