Your food is not good enough quality, even for an adult betta but especially for a growing betta. I would look for New Life Spectrum Grow formula, but at least normal NLS for bettas or Omega One.
Is this a new tank or was it already precycled 2 months before introducing fish?
They're cold. Increase temps to between 78-80 but only do it a degree per hour and make sure the heater is fully done heating and wait another hour before clicking it up again.
Are you saying all symptoms are gone?