Your cervical mucus/fertility cycles don't sound problematic to me. I do hear you saying you have dry days, just not like you maybe expect they should be, but unless you're trying to conceive right now, which you obviously aren't, fluctuations like this just aren't anything you need to trouble yourself with, including cycles where you might have skipped ovulating. That's not super-likely at your age, but it can happen, and when it does, it's usually just about something like a cycle where you had some extra stress, illness like a cold or flu, or other common, no-big-deal changes. It's also common to have a wonky month when it comes to how a period feels, what level of flow you have, etc. Bodies aren't machines: they vary.
Per the period difference, can I ask how long you've been having your periods for? And over the last six months, what numbers do you have for your cycles (how long has each been from day one of one period to day one of the next)? Do you have any other health issues that can create irregularity, like an eating disorder, thyroid issues, diabetes or endometriosis? have you checked in with a healthcare provider about the back pain and abdominal issues?