It is difficult to say what is happening alone with just the saliva microscope, as you are still waiting for AF. I have tracked my fertility signs including saliva ferning for the past 5 months (taking a break this month). What I have learnt is that you can also have full ferning several times during your cycle, inculding during AF and when PG. I would begin using it at about CD 7 till about 5DPO, when the ferning dissapears, then don't use it again till the next cycle. I was checking other signs as well, such as temping and OPK's. Temping was good as it told me when I had O'd, which corrolated with Ferning patters, I have not had much sucess with OPK.
It is possible to fall PG before AF arrives after PG, so the cramps and ferning could be PG or Oing. You will only know for sure when wither AF arrives, you get a +ve HPT. My only suggestion is you start checking your temps and see what they do over a period of time, it may give you more info.