If your doctor suspected cancer, why would they wait another two months to perform a follow up routine check?
They wouldn't. They would follow up with any tests they need on an urgent basis because they know they may need treatment to start as soon as possible.
You've given two possibilities. Did the doctor give these or did you decide on them? Are you aware of every potential issue that can cause this fluctuation? If not, which I suspect it's the case, this is anxiety latching onto your long term fears with Confirmation Bias.