@Kismett
There's likely to be a lot of chat about America & Things American online because it's the US who're currently holding the cultural imperialism baton AND Trump is apparently bent on offending & appalling literally the entire population of the globe before either he's voted out or finds himself ejected from office.
Then there are sadly always eejits about who'll merrily stereotype away about any & all comers. (Think the Canadians do best out of that game, because everyone says Canada's beautiful & everyone's really polite. Good work Canada's PR Department.) Anyone with two braincells to run together, however, should know that xenophobic stereotyping making sweeping generalisations about entire populations like that is ridiculous.
As a PP has mentioned, Londoners do hear an awful lot about how exceptionally subpar everything in the UK as. Most frequently - unfortunately for their fellow US citizens - from Americans who appear to be making a PSA about how Everything Is Bigger And Better In America for the benefit of everyone in a 5-mile radius. Mind you, it is not uncommon for people to think that you have a desperate yearning to hear them run your home into the ground on a more personal basis either. That doesn't make me dislike all Americans (or people of any other relevant nationalities!) though, just makes me think those particular ones are rather rude.
Unfortunately the brash-overbearing Americans are the ones who - for obvious reasons - get noticed & then recalled most in the collective, as well as personal, memory. And while London has heaps of Quiet Americans (as it were), people mostly won't register them unless they have sustained contact with them. And/or they'll assume they're Canadians. (Canada's PR Team really have done amazing work...).
Am sorry you've been having a rough time lately. I'm guessing if you've just moved here that seeing stuff online that seems anti-American will feel more raw/personal than if you'd read it while you were back in the States. Is there any kind of American ex-pat community where you are now? Just thinking people who know the acclimatising ropes where you physically are might be able to help/reassure you best. Do you belong to any organisation that has a global component to help you with getting settled? I know that's not what you're asking about, sorry, but was just thinking that maybe if you can feel part of your new community it might help squish the feeling that Everyone Hates Americans [And Thus You].
Be gentle with yourself.