The bleeding is from your hymen ("cherry") breaking and causing a little bleeding. This is just internal tissue trauma, and has no bearing on pregnancy whatsoever. The birth control method you're on is called depo provera (which is a long acting shot that lasts for 3 months), not the "drop shot" (just for your future reference so that other people know what you're talking about).
If you used a condom in addition to having an up-to-date depo shot, then you're fine. If you want to have a period, you can consider going on the pill, the patch, or the NuvaRing, which will let you have a period so you can monitor things more closely.
The bleeding means your hymen is now gone. If he only rubbed the tip of his penis the first time, you are on birth control, and he used a condom the second time...(and as long as the condom didn't break or slide off).. then you don't need to worry about being pregnant. You can still buy a pregnancy test from the drug store to ease your mind.