ArwenRivendell

I am a a junior at a hospital and was designated to give magnesium sulfate through the buttocks and I did make sure to palpate the hipbone to properly locate the right part to stick the needle. Now the part where I stuck the needle was a bit bruised from previous medication with the same medicine and the needle mark is still visible. So I decided to put it in between the two needle marks and I was sure that my location is correct. I did aspirate and when I saw there is no backflow I slowly administered the second dose without taking out the needle, my concern is when I removed the needle there was blood flowing out and I asked my senior about it and she asked me if I did Aspirate and I said yes there wasn't blood before and when i replaced the syrige there was blood. She checked on the patient and there is no sign that I hit the sciatic nerve. So she told me to go continue. I Did and after that I monitored the patient and she seemed fine and walking. Could someone explain Why was there blood? Because when i did administer it before other patients I didn't encounter this incident. Does it have something to do with the bruise?