I have abdominal pain on my left side and I am nauseas, is this a sign of diverticulitis?

Yes. Diverticulitis most commonly presents as left lower quadrant pain and fever. Nausea is less common, but can occur. These symptoms can also be seen in pelvic inflammatory disease.
No. If the pain is in the upper abdomen, this might be more reflective of gastritis or ulcer disease. If the pain is in the lower abdomen, diverticulitis could be possible but would usually be accompanied by diarrhea, not nausea.
Maybe. Diverticulitis is caused by the rupture of a small pocket on your large intestine, most commonly on the left lower abdomen. Symptoms may be mild-to-severe, depending on how well your body "band-aids" this rupture. The involved colon will thicken and often lead to the backup of intestinal contents, and thus cause bloating, nausea and/or vomiting. This is an infection; fever is common.