You did the right thing - stop immediately if you feel any twinges or tightening.
Weight lifting - even lighter weights - involves compression of the abdominal muscles. And some of them have been traumatized during the surgery, along with other delicate connective tissue and fascia.
You can easily tear a healing tissue 6 weeks after surgery. I blew out all kinds of things will one episode of straining during a bowel movement and required reparative urethral surgery.
Just be careful, go easy and please remember that your insides have been sliced and diced. I would concentrate more on aerobic exercise - walking on slight incline at various speeds. Breathing harder is a good way to get those abdominal and core muscles up to speed without putting undue, direct stress directly on them.
Also, I found seated weight lifting (overhead presses) with good back support, placed all the stress on my shoulders and I was able to ‘set’ my abdominal muscles more efficiently before each rep. Hope this helps.
Phil