So it sounds like you have already tried plans A, B and C. Psychiatric medication is plan D.
Don’t stress over whether he will need it forever. Think about what he needs right now.
The right medication could improve the situation enough to allow more time and effort for checking out other avenues (behavioral, medical, etc.) If you are considering a residential school/treatment center for your child, it means that things need to improve at home so that all of you can function as a family. Don’t think of medication as a bandaid, think of it as treating the most urgent problem first.
A good psychiatrist will not only work with you to prescribe whatever medications he/she thinks will work for your child, but will be open to supporting you as you try to find solutions for the underlying medical problems as well.
And as needs change, a good psychiatrist will change dosage/medication/etc. to best meet the current situation.