Pain in lower left abdomen, groin and back. What can this be? No problems urinating. Constant aching , pulling pain.

There's no way to say because there are too many possible reasons.
Groin pull is common, and involves the muscles that slant down from the edges to the groin.
Hernias of different kinds that may not show a bulge outwardly.
Sacral nerves wrap around from the back (sacro-iliac) to the front of the abdomen and then down to the groin, and might be irritated.
Bowel problem of various kinds - lower left is the end of the bowel.
And so on! Those are just some ideas.