I got my second treatment of Kybella Saturday morning. On Wednesday, will it be OK to go in an infrared sauna?

I would check with your board certified professional, but there should be no reason to worry about a sauna 4 days after Kybella -except: be aware that the area where kybella is administered may be numb ( like a "novacaine") for 3-4 weeks and you may not experience heat normally in that area- so you would need to be careful not to get a burn as a result of not feeling the heat.

I do not believe that going to a sauna 4 days after your Kybella treatment would affect your ultimate results, but it is possible that you still could have some swelling present in the neck and the sauna could worsen this.  

I recommend that my patients take it easy for 24 hours after their Kybella injections.  Going to the sauna a few days after your injection won't have any effects on your results.