Separate beds. We always knew Pete had a kinky side.
Seriously, Bert, Ari already touched on my first thought - wondering whether you might be taking aspirin (as some people do at low doses for heart health). Aspirin is a blood thinner, and those who take it on a regular basis are often more prone to bruising, as are people who take Coumadin (a blood thinner).
My next thought was, "Why the quads?" Quad shots are best if you have to do them yourself, since the average person who works out at all has less fatty tissue there. (I usually recommend quad shots for those who self-inject because you get a better angle and can aspirate the needle more safely than you can with your own delts or glutes.)
With only a 1/2 cc injection, I'd recommend trying the delts or, since you're prone to bruising, the glutes next time. (Not to mention that they have less nerve endings than the quads, so you're in for a less painful shot.)