Why is it so many people are ignorant of or do not follow simple RICER principles. Even though I do not suggest people self diagnose themselves using google, even a simple internet search wil give you how to deal with a muscle strain and guess what it is... RICER.
Rest
Ice
Compression
Elevation
Referral
Why the hell are you applying heat to a muscle injury after training and less than 48 hours after an injury?
And rest. For gods sake rest. You don't have to become a couch potato, but at least avoid exercises that involve whatever you have injured.
And yes that referral part. Depending on the severity and whether you make it worse by continuing to train as usual you may need to see a good physio.