I must've traveled through a time portal, suddenly it went from being 3 months old to 4 months old. I guess you found out the hard way by phone support telling you when it expired, which is at 90 days...3 months...so...if it's 4 months old how did your phone support expire after 60 days instead of 90? 😉 It can be frustrating if you're so frantic that you're unable to deal with and relay the problem calmly and accurately.
I assume you don't have an Apple Store anywhere nearby? If you do then a "Genius" will be able to take a look at it since it's still under warranty.
I don't think you answered whether or not you have any other wifi-enabled devices or not and if you do if they, too, have problems connecting to your wifi. That would help nail down if the problem is with the Mac or your wifi.
Take a deep breath, calm down, and relax. Stressing about it won't get it fixed any faster.