Alex, get to an otolaryngology voice expert.
Sounds like you know now what your technique should be, but often musical theater singers BELT too much!
You could have already caused nodes or scars on the vocal folds.
Bel canto technique gets volume by floating the sound on well sustained volumes of air, rather than pushing against the vocal folds. That pushing to get volume sounds like it may be the problem. Stop speaking, write to communicate, get to an expert doctor and don't sacrifice your whole life long use of voice just for using it short term now.

PM me if you'd like.

Alice