TTC Question

Marie
I've been on Metformin for 6 weeks now (up to 2000mg now). AF didn't come as scheduled so I ended up taking a 10-day cycle of Provera which ended last Thursday. AF showed up yesterday. My question is, because my periods are so irregular (My last three were in August 2015, January 2016, and then this one in March 2016), how do I know when we should be TTC? I'm assuming the normal time frame doesn't apply. Thanks!