Is there a way?

So, I haven't missed a period yet. it is said to be in about 8 days but my periods are irregular. (Small Backstory though: I was pregnant 2 years ago and miscarried) I am now having the same symptoms I did when I was pregnant then and I am just wanting to know, how soon is it okay to take hpt? I haven't talked to anyone but my sister in law about this and I am honestly trying to stay positive because we want a baby so bad.