With previous waves you were likely to become PCR negative around 2-3 weeks after initial infection, though it was longer for some people. We don't have data f

With previous waves you were likely to become PCR negative around 2-3 weeks after initial infection, though it was longer for some people. We don't have data for omicron yet on this. As for whether you have omicron - that depends on the precise test the lab runs. Many UK labs test for three covid genes - S, N and Orf. Delta was S-gene positive. Omicron is S-gene negative but N and Orf positive. If the test is S-gene negative (often reported as S-gene target failure, SGTF), you can be pretty sure it's Omicron at the moment. Alpha was also SGTF, but isn't really circulating anymore.