Nausea, diareah once, right side pain that feels like muscle spasms 35 weeks pregnant! what could this be?

Many things: You should be calling your obgyn with this problem immediately so you can be evaluated, this is not a question to be answered on this web site, it may or may not be serious but it should be evauated.

Appendicitis, gastro: Gastroenteritis (mesenteric lymphadenitis) and acute appendicitis could cause these symptoms, however appendicitis would also cause anorexia/no appetite. Seek medical care if these symptoms persist and/or do not improve within 12 hours! differential diagnosis includes urolithiasia/colic, right adnexal torsion, and many other less likely culprits.