I think my computer was hacked. Please help me

So earlier today, I was using my macbook pro when a message popped up that said something like "someone is accessing your ip" or "your ip is being used" or something along those lines. I thought nothing of it at first, but then about 2-3 hours later in the day, when I went to log on Facebook my Facebook had been hacked, and it doesnt seem like a coincidence that this thing popped up earlier. What do I do??

G'day and welcome to the forums.

Change the network password and use a 13 digit alphabetical/numerical passwords with some capitals and symbols. Your router user guide will show you about setting up a password, also remember to change it to the same In System Preferences > Network. As for facebook, you goes there at your own risk, It is often hacked so change password there and make it a unique password.

From your description, it seems clear that someone guessed your (probably very simple) Facebook password, which has absolutely nothing to do with your computer.