Hello everyone, 36M and new to IF

I lost 70obs with Noom (calorie counting) but due to a severe back injury and I think medication, I put it all back on.

My ability to workout has diminished a lot while I wait for surgery, however I decided to try IF as it's working for my sister. I am doing 16:8 and try to eat around 2000-2500 cal per day, while I do mild bike cardio and sauna 3-5 times per week and burn on average 600cal / session.

My question this. Last week I lost 14lbs, this week I've put 4 back on and seem to be climbing around 1lbs per day. I don't think I'm doing much different and I'm wonder if the Gabapentin I'm taking may be causing this.

Any insight, or tips/tricks would be appreciated.