Just keep trying to up the volume! And yeah, fly's can be tough on your shoulders, but you should be trying to workout so you're balancing your force couples. Do some fly's if you want, just watch how much internal vs external rotationally dominant movmnts you're doing.
If you're not doing stuff like face pulls, good, strict, seated rows, db rows, some incline pushups with a nice hold at the top, you're setting yourself for a GIRD (and bear with me on this) Glenohumeral Internal Roatational Deficit, or something along those lines.
A lot of the questions about how much is enough, whether is be with pain or volume is a totally personal question; based on muscle fiber makeup, diet, sleep patterns, micro and macro-nutrient intake, etc, etc.
A good measure of whether it's working or not is, "are you getting stronger"? If not, you may need to modify one of the variable in that great list of things one must to to grow.