I'm soooo sick of it...

My body has evidently decided to do a total flip-flop on me. For years I had very predictable PMS-symptoms. I would feel depressed, teary, fatigued, bloated, etc during the week before my period. And then, once my period started, I would feel great again.
But now.... I feel at my BEST the days before my period, and instead I totally crash when my period starts and it continues afterwards. My last period started night between Sunday and Monday and today I feel like literal crap...

My stomach actually behaved pretty well for a few days before my period. I would have nice normal shaped BMs, but as soon as my period started I had diarreah (which is actually normal for me). I'm still not back to good BMs, and today has been a day of loose stools. One of my first thoughts when I wake up is, literally, "I wonder what my pooh will be like today?" And
that can't be good for any kind of stress-induced stomach problems, if that is what I have...
Anyone else who has experienced this crazy flip-flop of symptoms, or anyone who has a reasonable explaination for it? It's definetely one of those days when I feel so sad, scared and lonely...