FINCHforum

She laid a clutch of 5 a week or so ago, didn't sit, was no new eggs for 3 days so I removed them. A day later she started laying again, 3 eggs so far, 4th egg was expected last night but it didn't come, it's now into the evening and still no 4th egg. The hen seems to be breathing heavily, she doesn't look ill or anything, but something doesn't seem right, she's sat on the perch and acting normal, just a lot of very heavy breathing going on. I don't know if she could be eggbound or not.

Sounds like heavy labor. If she cannot pass the egg she will become eggbound. Add a light for heat to the cage. Add calcium plus/ calciboost type product to the water.
Sometimes the hen will pass the egg and be fine. Sometimes each egg after that will cause problems. In the later case rest the hen and wait for health/diet/condition to improve before trying again.
If she is moulting then do not breed. The energy for moulting and egglaying are too much for her.
Hope she recovers soon.

I agree with Candace [add a heatlamp and calcium]. I hope it works out for you.