Severe shoulder pain

So I strained my shoulder and it is spasming terribly... feels like it is broken the pain is so bad. Is Tylenol 3 safe to take PRN? I deal with the pain more often than not with heat and icy hot, but at night is when it is so bad I am not sleeping... If I take 1 tablet a day for a few days until it gets better is this safe? I say 1 because I wait until I am in tears and complete agony and I will only allow myself a half a tablet when it is this bad.

my dr told me strictly tylenol. she said if the pain is really unbearable the most she would allow me to take is 3 extra strength a day but NO MORE. one in the morning, one at lunch, and one after dinner and to try to wait at least 6 hours in between each one