confused!!!

hey ladies I'm new to working all this app stuff dpo stuff etc me an hubby been ttc since Feb #1 baby! my periods are 28days theyusually last for 4 days each month I have not had a period since 8th august which only lasted till 10th august can any ladies give me some advice on when I should test etc I have done couple tests but were negative maybe I have worked it out wrong an my period is not late? just seems long time between cycles sorry for long post just bit confused