SAN DIEGO — San Diego County is still investigating what gave dozens of people diarrhea at one of the city’s designated camping areas for homeless residents, but officials said nobody was hospitalized and there were no new cases. Around 30 people and four staffers fell ill last week at O Lot, near Balboa Park, prompting an inquiry by the environmental health and quality department. One of the site’s operators, the nonprofit Dreams for Change, reported no new illnesses as of Tuesday, according to city spokesperson Matt Hoffman. The majority of those sickened were “feeling better” and the four s…