It looks like a bruise. It may be lingering around because you have a concentrated little area of blood under the skin. Anytime you get an injection you run the risk of getting a bruise. Injections are made with a needle which can puncture a tiny blood vessel under the skin. A small amount of blood leaks out of the vessel and causes the bruise (blood under the skin). The tiny blood vessels are not visible, so anyone can get unlucky and have one. Injecting fillers is an art. As a physician you are trying for the best result possible. Sometimes you can get that with a cannula( blunt needle) so it bruises less because it tends to push the blood vessel away as opposed to puncturing it. In many cases you cannot get a great result unless you use a needle to get the material in the best location.I recommend massaging the bruised area to get the blood under the skin spread out so that your body will get rid of the bruise faster. Once you start doing that it should get better much faster. If you are worried have your injector check it out since all experienced injectors have dealt with this issue........... that nobody likes.