I think I might be the bearer of bad news for you.
Once the paint starts to "blister" there is very little you can do to repair the problem other than removing the paint and starting again.
The reason this blistering happens is because of poor prep. work when it was painted in the past, most often bathrooms have a tremendous amount of steam and naturally water vapor, this vapor is absorbed by the paint and then as the paint dries out it shrinks and alas there are the cracks. No matter how many coats of paint you put over this problem in a reasonably short period of time the problem will show it's face again.
The number one thing all bathrooms must have as a primer is a paint that also acts as a vapor barrier thus stopping the drywall/plaster from absorbing the moisture and setting in motion the cracking problem.
I have had some success with skim coating the entire ceiling with drywall compound and then applying Zinsser (an oil based primer available at most hardware stores) then two top coats of the paint and color you like.
Unfortunatley little else is going to solve your problem.
As it's an apartment and you don't want to spend a great deal of your money and or time, if it were me I'd scrap back the ceiling as best you can give it a coat of Zinsser and then the finishing coats, it won't look like a perfect flat ceiling but it will probably look a sight better.
