door lock sticking with key and from inside

ok here’s the problem. I have a '91 GS and lately when I try to lock or unlock the doors it’s been seeming like it’s resisting a whole lot. Tonight when I tried to unlock it wouldn’t even unlock. After I got inside and worked the inside lock a few times it would unlock from the outside. The fact that we had a freeze might have something to do with it but the passenger lock worked really good (as always). I did a search but I didn’t find anything that really matched what was wrong with my car. My dad said he put some door lock stuff on it and it worked for awhile but it’s back to sucking. I know it’s not a bad key or anything since the key works fine on the other door. I just want to know if I should fix it or should go get another lock?

sorry if I missed something when I searched.

wd40 and de-icer.