how long on tamox?

Hello Ladies

I had chemo starting last July, after first chemo my periods stopped.
Once chemo finished I was given tamoxifen started it in November.
I haven’t had a period since.
When I last saw oncologist he sent me for blood tests to check my hormone levels to see where I am in the menopause.
He thinks I might be through it, has anyone got through menopause that quickly, I thought it would take about 4 years?