Is it possible to get a BFN one day and a BFP the next?

Ami • Trying to conceive Baby #4!
Please help. I'm pretty sure I'm pregnant, but my periods are so irregular that I have no idea when to test. I'm burning through First Response and Clear Blue's HPTs! About to lose hope. (I say I'm pretty sure because I have 3 kidos...all the same symptoms, and pretty obvious symptoms) I tested today: 11 DPO--BFN. When should I test again? PLEASE HELP!

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