Am i pregnant?!

Okay, so me and my partner have been trying to concieve after having a miscarriage in may. I always have irregular periods so find it really hard to work out when im ovulating. But recently i have been alot more tired recently, i have a nauxious feeling pretty much all the time, stomach cramps and major headaches. My boobs have changed, they are harder than usual and my nipples feel tingly, sorry for the tmi. I did a pregnancy test earlier today and it came back invalid. Is there anybody else out there that's in the same position as me? What do you guys think? Could this finally be the time?