A lot of authors are unclear regarding when to capitalize a title or profession. The rule is pretty simple. When you are using names of affection, like honey, sweetie, sis, etc., you keep them lowercase. When using titles in direct address, you capitalize them.
I don’t understand, Doctor.
Will you tell me, Captain, when we will get there?
Your tests are too hard, Professor.
I talked to Mom today.
One tip to help you know when to capitalize is if you see the word the (or another article) before the term, you lowercase that term.
The doctor told me I was overweight.
I spoke to the captain and he said we were almost there.
My professor is really tough.
I talked to my mom today.