Can this be implantation bleeding ??

Leia
I need help I'm having irregular periods and I'm ttc things are happening and have no idea what's going on ... My last cycle was 27 days period lasted 4days ..all fine ..I'm now on cycle day 20 and I  started spotting on cycle day 18 its its very light it on day one it was pinkish , then it's more brown sorry if tmi and only when I wipe an gain tmi ..  11 days until next period when should I do a pregnancy test as I have no idea when period is going to start due to irregularity ? Thankyou xx