Celebrex is an NSAID, an anti-inflammatory.
Zoloft is not, so you need to keep taking that.
I think that time, together with rest, elevation and icing when you can, will eventually cure your kneecap pain, as the swelling goes down.
Try to remember that complete recovery from a knee replacement does take a full year, and you are not yet 4 months into that - only a third of the way to full healing. There's still plenty of time for much more improvement.
Your knee won't always feel as it does now. It's still a work in progress, not the finished article.
For pain, it's safe to take Tylenol (Acetaminophen) 1,000 mg 6-hourly, to a maximum dose of 4,000 mg in each 24 hours.
Do check any other medication you're taking, such as cold cures, to make sure there is no Acetaminophen/Tylenol in them. If there is, cut down one or two of your other doses, so you stay within that safe daily limit of 4,000 mg.