Am I going crazy?

I'll try to keep it short..
For about 2-3 months now, I've been feeling like I'm pregnant. I've taken multiple tests, but they're always either negative or show a very faint/nearly invisible line. I've tried different brands...
I haven't had a period for 1.5 years because I'm still breastfeeding.. I tested a lot in the first few weeks but then tried to put it out of my mind and ignore the symptoms. But after a few weeks, I took another test and it seemed like I had that very faint line again. I took a digital test, and it says not pregnant! I just feel so strongly that I'm pregnant, and I don't know what to do anymore!
I also want to mention that we're not trying at all. I thought maybe I'm pregnant with phantom pregnancy, but that seems crazy too..
Right now, I have severe labor-like pain in my lower back and upper thighs, fatigue, and waves of nausea. By the way, I've had the nausea and fatigue since the beginning, which is why I took the first test.. sometimes small stabs and pulling in my belly and lower abdomen (really all the way down) seems to be... getting bigger? I also have little appetite but feel hungry, and I get heeeeeeeen very irritated/emotional. I also get sick from the smell of my boyfriend's (smoke) where I never had issues before. And other small things I recognize from when I was pregnant with my previous baby.. am I going crazy or could something else be going on??
Thanks for reading, I'd love to hear what others think about this!!