exact same thing happened to me injecting quad a few days ago . but i never had much blood , my guess i that the reason it hurt more and u had more blood is that u went through a vein . i had swelling , and the day after a big red spot on my leg under the injection site that felt swollen , bruised and a little hot and itchy . also the wierd thing is , another wierd thing is that i got a bruise all the way down by my knee cap and i couldnt walk the next day very well . you probably just injected to fast , or if u didnt just went through a vein . can cause bruising , red spots and pain , went away for me in 3-4 days .