You need to see a doctor as soon as possible especially if it continues to get worse.
It it looks like a "Bulls-eye" there is a good chance you have been bitten by a tick carrying lyme disease and require antibiotics to avoid a lifetime of misery. Look up images of what a lyme disease bite appears on the internet and see a physician immediately if you suspect this is the problem. There is a window of opportunity for treating such infections before the problem becomes systemic.