From what I read, you are fully vaccinated, getting the booster adds duration to the protection, however the Delta variant seems to have the ability to spread cell to cell via contact through cell membrane transmission. This allows virus particles to infect new cells without being exposed to antibody virus particle neutralization. The cells still expose surface infection markers = the immune system still kills those cells. These cells infected still burst and spread virus particles however the infection does not progress to a severe infection unless you have the so-called Covid co-morbidities. This site explores these aspects.
https://www.cdc.gov/coronavirus/2019-ncov/hcp/clinical-care/...
You should get tested ASAP if you have symptoms so the correct treatment can be started. These treatments are sensitive to the time stage of your infection = several have time windows when treatments are either too early, too late - or just right for the best outcome.
Covid treatment timeline is important - do not miss one.
Here is a dense read of various aspects if you are hospitalized - hopefully your medical center can rapidly test and stage you and may be able to avoid hospitalization.
https://www.uptodate.com/contents/covid-19-management-in-hos...