Had an appendectomy 2.5 weeks ago. Did heavy lifting 2 days ago; now abdomen hurts. More pain plus gas and bloating after eating now. Should I worry?

Probably not but.... If you are passing gas and having bowel movements that is reassuring but in anyone with recent surgery who finds themselves suddenly having worsening abdominal pain it would be prudent to see their primary care provider or general surgeon who did the surgery if the pain worsens or persists.
Probably ok. You are probably ok. If you see a bulge around your incision, or if the pain doesnt go away , go back and see your surgeon.
Possibly. You do not mention what technique was done, but if you lifted something and tore a stitch, it could be a problem. The gas and bloating could be normal, but if it seems worse, be seen by your surgeon.