You're totally normal. Don't be worried! (That's natural, of course... to be worried.) Switching pills can definitely be a part of the cause. Hormonal changes and such. I went through something similar, and now I only get a period about once a year, even though I'm on monthly pills. It's actually quite nice. =^)
I would advise you to go in and see your ob/gyn, just to make sure everything is in order. With me, my random spotting and clotting was due to a thin uterine lining. Any time I would exercise or engage in *frisky activity* (hee-hee!) I would spot... and sometimes clot. Ugh. It was nas-tay.
My ob/gyn put me on a bit of estrogen for a while, just to build the lining back up. No one wants to be on that for too long with all the risks associated, so once it was back to normal I came off... and then didn't have a period! For over a year! My ob/gyn checked me and said everything is normal, and that sometimes this. just. happens. No cause for concern. I've stayed current with my yearly exams, and all is fine. I usually get a period around September, but we're done having kiddos, so it's rather nice to not have to worry about it.
If you ARE wanting to have periods in the future (you may NOT be done having kiddos), my ob/gyn DID tell me that going off the pill altogether would bring my periods back. (No thank you!) I'm not saying this will happen with you, but if this is indeed a hormone thing, then it most likely will.
I hope I've been helpful! I know it can be stressful walking through this, not sure of what exactly is going on. But, if you've been checked out and everything is clear, I say enjoy it, sweetie!