The pain feels like contractions i've had 3 kids the pain started like a month ago but it's getting worse and it also hurts on my left side don't know if i might have a fallopian tube pregnancy i'm using nexplanon

Check pregnancy: You need a pregnancy test immediately. If the pain is severe you need to see a doctor right away. It could be a twisted ovary or other serious problem.

Pregnancy test: will be required to answer your question and if positive needs urgent medical attention to exclude ectopic pregnancy. If negative then still would be worth assessment with a doctor to sort it out.

GYN exam: Including PAP, ultrasound pelvic exam , pregnancy hormone and thyroid and blood sugar with HgbA1c studies would be a good start.

Better get checked: Tubal pregnancy, or any ectopic pregnancy if gets disturbed usually doesn't cause contractions, and if on nexplanon you are unlikely to ovulate, so very rare to be a tubal pregnancy, can still be your uterus or your ovary though. Other organs as kidneys, ureters, colon, can be the cause, hence the need for medical attention, see your doctor or go to urgent care / ER, good luck