I believe I have a morning glory, but that's not the question. What is eating away at my leaves

If you shine a flashlight through from the back of the leaves can you see any insect larvae inside the damaged areas? (Leafminer).

No

Here's a closers look

If you can't see anything inside the thin areas of the leaf, and there aren't any caterpillars (often very small green ones) on the back of the leaf, it may be that whatever it is has done the damage and moved on. The newer leaves don't look as bad, are you still seeing any new damage on those? I don't think it's a disease but some kind of chewing insect.