Advice to those using Clearblue digital! :-)

So, I'm 15dpo. Today I have taken 3 tests, 2 said 'not pregnant' and one said 'pregnant 1-2 weeks' now after some investigation I have found that clear blue have recently updated their tests. The old ones are not working for me, and the new ones are. You can tell which is which, the serial number on the box will start with an 'M' if it's the new type, or 'C' with the old types. Hope this helps relieves someone's worry someday as I've had an awful day panicking it was a chemical pregnancy x