I got stung by a wasp 2 days ago on the back of both ankles, and the itching & swelling is getting worse even when taking benadryl. should i go to er?

Yes: The wound may have gotten infected, or inflammation is severe enough to require prescription meds as steroids, hope the reaction was only in your ankle, and didn't spread, if otherwise , you want to see an allergist for evaluation. Hope also it was just a wasp that stung you twice in two different sites, and not something else, best wishes