How much time were you using the heating pad vs actually stretching?
Personally, I use one of those moveable shower heads on the cord, you know the kind, and then just sit on the edge of the tub with that shit blasting my junk at full heat for anywhere from at least 5 -10 minutes, while doing some light stretching at the same time, then I go into the [words=http://www.mattersofsize.com/forum/showthread.php?83577-Length-master-official-order-thread-now-shipping-06-16-2014!!!]
LM[/words] and do a length session for 30 minutes, and I'm still pretty warm after that, just as long as the AC is off and the fan is off too. I just don't think I get anywhere near as good a stretch or as warmed up as I do with any other method, having tried the heating pad, but like you said, everyone is different.