Hi, Izabel, sorry to be late in responding -- I was away for the weekend. You've gotten great advice already. I have had Plantar Fascitis several times. The first time and the most recent time a couple of years ago were the worst. The other times, I was able to successfully get relief with the ice and stretching exercises you're already using. (Yes, I was advised to use a Coke bottle for the shape, but it sounds like you're getting a similar benefit from the 7-Up bottle. )
The first time I experienced plantar fascitis, I was training for a marathon and got an injection into my arch to ease the pain, then I was prescribed the ice and stretching. The most recent time I experienced it, ice and stretching didn't help, so my ortho recommended a night brace. I found one that wasn't too obstructive on Amazon for about $20, and after about a month of wearing it to bed at night and doing the stretches, I obtained relief.
I hope you'll be painfree soon!