Positive OPKs cd 13 & 18 ?

[mummof1]

What should I make of a pos opk cd 13 followed by neg on cd 14 and 15 to then a really strong pos cd 18 ?
Here's the two tests

 

[missa_81]

I have some that look like that. Is it a positive? I had one similar to that this morn and then a much lighter one just now.

 

[mummof1]

I believe these are both positive , the other ones the test lines were very light ! I'm just unsure why i would get a positive then negative and then positive again 5 days later