I had to self-isoate until I got a negative result from the PCR test.
I had to stay in a hotel room by myself until my PCR test came back negative.
ーI had to self-isolate until I got a negative result from the PCR test.
「PCR検査で陰性の結果が出るまで自主隔離しなければいけなかった」
to self-isolate で「自主隔離する」
until I get a negative result で「陰性の結果が出るまで」
ーI had to stay in a hotel room by myself until my PCR test came back negative.
「PCR検査が陰性の結果で戻ってくるまで、私一人でホテルの一室に滞在しないといけなかった」
to stay in a hotel room by myself で「私一人でホテルの一室に滞在する」
to come back negative で「(検査の)陰性結果が戻ってくる」=「陰性結果が出る」
ご参考まで!