Need advice

So me and my husband are trying for a baby, it's our first month trying and I'm not sure if we are expecting or not I've tested but still think if I am pregnant I'm too early. But I am having some cramping and I don't think AF should be coming until next week sometime. If I'm not this month we will just try again, but my question is, how do you know when you obvulate with very irregular periods? Mines never on time, I never have been able to figure out my cycle days cause it's all over the place. I could go months without one or have one on time every month. I need some help!