Period came three weeks early and pelvic pain with nauseau but not pregnant per hospital. Found cyst on left ovary and left tube removed. Whats wrong?

Ovarian cyst. Usually a cyst forms on the ovary from its normal function "functional ovarian cyst". You'll miss an ovulation or ovulate late, or the cyst that forms after ovulation (corpus luteum) doesn't go away like it should and it delays your cycle. Either way, it usually causes irregular bleeding. Nausea is common. It will usually resolve on its own with time. Recheck an ultrasound in about 6 weeks.
May be the cyst. Sometimes a cyst can disrupt normal menstrual cycling. Since they usually produce estrogen (at least, functional cysts do) they may also cause some nausea.