You can hear it up. It will lower the viscosity and help the oil to absorb into the muscle. Often times, you can get what is called test flu. Your body reads the hormone as a foreign body and tries to figut it off like it would a bug. The immune response is what makes you feel this way. After several shots, it will clear up. Heating the oil may have helped your body accept the injections better, but there is a good chance that they would stopped eventually anyway. This is more common with fast acting gear like prop than it is with long esters. 

Just dont heat the oil up too much or you can burn yourself