Unsure when to take pregnancy test as periods are irregular....HELP!?

Me and my husband are tryig to concieve baby no.3. We have only bee trying this cycle since we have a 8 month old son, since having my son my periods have been anywhere between 24 and 32 days apart. So my last period was the 27th may and im unsure about the period before that but i think it was around the begging of may. We had sex everynight from the 2nd until 6th bt for the last 4-5 days i have had cramping in my lower stomach behind pubic bone and aching cramps in my lower back. My breast arent sore as they were when i concieved my youngest child but my nipples are really tingly almost as if they are on fire, now because im unsure when my eriod is due i have been testing every morning using early hpt for the last 2 days with negative results both times. I was just wondering in your ladies experience when u think would be best to test again to avoid dissapointment. I feel as if i wouldnt be lucky to fall pregnant the first time we tried but there are a few familiar feelings from my previous pregnancy and cant help but get my hopes up and every negative test feels like someone is ripping out my heart... HELP PLEASE x