Periods very irregular hard to know ovulation any advice ?

Hi there me and my husband are trying to conceive I got my copper coil removed 2 months ago and was disappointed when i got my period last month. I know we haven't been trying for very long but we are both relatively healthy and in our early mid 20s. My periods have always been very irregular some months they come early and others it is late. So I'm unsure of fertile days I have been taking ovulation tests this month and they have all been negative, I can't help to think there something might be wrong as before I used to get very painful very heavy periods to the point I would pass out or be physically sick and always get bad diarrhoea on my period days. Any other women been through similar ? Would be great help for any advice. Thank you ladies