Hello hellolove. Welcome to the Library. I hope you find what you're looking for.

I'm just one voice of many, but if I were cornered into making distinctions between the terms you listed I would say:
A masochist gains especial enjoyment from pain and suffering
A bottom enjoys some combination of pain & suffering with being dominated/forced into particular actions or situations in the context of the bedroom
A submissive enjoys some degree of surrender of willpower/self determination to his or her dominant

Again, just one man and no kind of real authority :P