TTC after Mirena

I had my mirena removed a little over 3 months ago, and had high hopes we would conceive quickly. I joined glow not knowing how many days are in my cycle and not knowing the norm for my period. I know it learns the more I chart. My periods are not consistent. My first was 4 days from the 14 to the 18th, the next month is was the 18th to the 21st(and was extremely heavy) and then this month I still haven't gotten my period. I tried ovulation testing every day last month and got nothing. So I am basically trying to conceive based from my ovulation days Glow provides me. Is there anything I can do to improve accuracy? I still don't know how many days my cycle actually is. Any advice is appreciated. Thank you!