So ive gone through about 3 tubes in the last week. I have a 700c continental Gatorskin tire on a Ritchie Aero OCR rim. This is the rear wheel. The tube is a generic 700x19-23.

There are no punctures or damages on the tire, inside or out. The other day I got a snakebite, probably due to underinflation. I replaced the tube today, carefully, inflated to proper pressure, and rode around for a couple hours. Everything was fine, I kept glancing at the tire to make sure there was no immediate leakage, everything seemed perfectly fine. I didn't hit anything, no glass, no potholes, no bumps. After I got off the bike I fingered the tire, and it felt like no air had escaped at all.

After I'm done riding, I leave the bike in my room for about an hour, and when I come back, the rear tire is flat again. I take off the tire, take out the tube, and - what? I dont see anything. I pump up the tube until it is as fat as a donut, I dont hear anything, I dont see anything. I was going to put the tube underwater to see if theres a leak, but then my ****ing pump broke

I have thoroughly checked the tire and the rim. The tire is fine, the rim is fine, the rim tape is fine, both are clean on the inside, theres no debris or dirt, they are ****ing SPOTLESS.

WTF is going on here? I know the tube must be punctured somewhere, although with a very, very, very small hole. I'm tired of buying new tubes. Am I using the wrong size tube? somebody tell me what I'm doing wrong.