The reason you don't reuse needles is because there only designed for single use. Try this, stick yourself with a fresh needle, then get a new needle or the same one and stick it into the rubber stopper of a vial about 3 times then stick yourself and you will notice a big difference, the smaller and sharper a needle is the less it hurts but the more easily it blunts.
I got a bruise 1st time I injected, not sure if I hit a blood vessel or not, but I have noticed blood a few times and have never got a bruise from it, there are 2 tricks to not getting a bruise, 1stly take it out the same angle you put it in, and don't move it around once its in, so be careful if you aspirate. I stick it in slowly but take it out fast, thats what works for me. Another trick is to rub the area in a circle after injection, I guess you should do this if you see blood, I assume this works on the same principle to why you hold down an injection site after you get a drip or needle in your vein, and it really works, I have had drips before and once I didn't hold it down and I had a huge bruise. Now I always make sure I hold it down and have never got a bruise from drips or blood work.