Don't worry too much about it. Check the symptoms:

Red area around injection site
Hot to the touch
Fever

Are usually signs of infection/contamination. If it's just throbbing, then what I'm guessing is on your first injection, you did it 90-100% perfectly and minimized the pain. Then when it came time for the next injection, you felt more confident and it was just a bother to you, so you didn't heat it up, stuck yourself too quickly, wiggled the pin around in the muscle and most of all: INJECTED TOO QUICKLY!!! That seems to be THE deciding factor in pain the day after injection.

Prop will always have a bite too it, but Test Enanthate shouldn't be much of a problem at all, shouldn't be "throbbing" anyway. Wait it out 1-2 more days filled with Ibuprofen (I pop up to a gram at a time... and no I'm not running ANY orals) and 30 min. on heating pad, 30 min. off it. Like I said, I think you'll be ok. Heat and anti-inflammatories will ease the pain while you wait.

You'll more than likely be just fine. Good luck with everything.