AF three days late - when to test again?

Got overexcited and tested on the day of glow predicted af start and straight again the next morning... both negative as far as I could make out. now I want to avoid another disappointment! Af normally v regular - not a lot of other symptoms, except excess saliva building up in my mouth all the time.... any tips or support to help me through? Had a mc in April, so scared it could happen again :(

Thanks for any advice!