As a start, "must" is used when it is an obligation from yourself:
I must eat to survive.
But it can also be used to mean a strong advice, as :
You must see this film, I liked it so much !!
"have to" is used when someone forces you to do something:
I have to clean my room to go out (because my parents want me to).
"will" is simple future, so it is a fact that you will do something:
I will work tonight (it is something I'm sure I'll do, because it is planned).
"should" is advice:
You should work harder to succeed.
and "would" is conditional (generally with an if):
I would be happy if I found someone.
So here, it looks like a simple advice, so, "you should see", but it is not part of your possible answers...
The problem with "should have seen" is that it is advice, but it also means that you didn't do it, and it is too late to do so.
The sentence would have been :
You should have seen a doctor, and have had some rest
So it is an incorrect answer
So here the answer must be "must see".