It could certainly be BPD. There is a lot of overlap between BP and BPD. I currently have one pdoc who says I have BP and another who says BPD. I've seen a lot of people on these boards who were first diagnosed with one and then it changed to the other.

My opinion on your history:
1. pwBPD have emotional dysregulation that is not cyclical. Moods can fluctuate rapidly.
2. A sign of BPD is impulsivity. This could be what was going on with your shopping addiction.
3. The overthinking sounds like anxiety. When I'm depressed/anxious I isolate which provides the environment for upsetting or racing thoughts.
4. Emotional outbursts are obviously a part of BPD. I think it's normal to have a period of catharsis afterwards.
5. I'm interested in hearing more about your psychotic episodes. I have had auditory and olfactory hallucinations. I also had a period of 3 weeks in the hospital where I had a breakdown and acted out of character making threatening phone calls daily. I have no memory of this. BPD can include psychotic features.
6. More emotional dysregulation. BPD.
7. Sleep effects my mood too.
8. Sounds like either depression or maybe something medical going on.
9. Could be some type of dissociation going on. BPD. Could be a subconscious fear of abandonment/rejection that made you isolate.
10. My mood swings are almost always a product of spending time with other people. My rages are only because of my relationships.

Can I ask you if you have a history of trauma? PTSD and BPD go hand in hand.