Extreme lag MacBook Pro

I have a macbook pro 13" unibody mid 2012 model ibe had it for roughly 4 years now

Today i started up my mac and it took 30min for it just to start up and load the log in screen and i fell asleep multiple times during start up. Once it started up i typed in my password and it took about 30min to log in. Then once i was finnaly logged in simply opening a folder caused it to experience more extreme lag again taking about 30min to open the folder.

I have taken the laptop to a guy twice for other problems and he said that he "rebuilt the harddrive" anyone now what this means???

Also before this when playing videos the video would freeze continue to play audio then skip 10-20 minutes of video then continue to play as normal

Is there a way yo fix this lag preferably without losing my data because not all of it is backed up

Or should i just replace the harddrive

PS i would prefer not to take it to apple because the first time i took my laptop to them they fixed nothing and charged us about $100-$200