as mentioned there are a couple possibilities
-too much BA (most likely, often the case with prop)
-youre allergic to the carrier oil or ethyl oleate (if its inside)
-too little solvent so that the gear crashes inside of your muscle (unlikely if it doesnt crash at room temperature but not impossible)
-you pinned too much (some people can only take like 1-1.5ml into delts) or pinned the same spot too often or simply hit a bad spot (close to a nerve or whatever)