Help me

Okay so my cycle is irregular. Af could arrive on the 4th week to the 6th week of my cycle. I just looked and according to this app I will be on my 4th week in this cycle on Thursday (counting from the first day of my last period). I am positive I conceived this month as I'm experiencing an array of symptoms (same ones from my first pregnancy no matter how unsuccessful). According to this app I'm due af on Wednesday. When should I test for pregnancy because I dont know when or if I miss my period bc my cycle is irregular. On my first I got a positive the third week of my cycle (miscarried at exactly 6 weeks) and when I got pregnant again I didnt get a positive test but I miscarried around 7 weeks and 3 days.