I had a dr that could not medicate me effectively try to say I had BPD. I guess amny bpers are also bpds. I am not bpd, doesn't fit me at all. If it fits you, work on it and Good Luck.
Bipolar and Borderline occur together a lot believe it or not. I was diagnosed as Borderline at one point. The two are pretty similar, and as with anything else only a psychiatrist could diagnose you. I think this is even more true with personality disorders. If anyone with bipolar looks at the criteria of borderline you'll find most of them fit most of the criteria of it. They are so similar a lot of psychiatrists have trouble telling them apart in a lot of patients, and some even think that they're related.
So yes, it's very possible to be diagnosed with both of them.
I think anything is possible, you can have manic episodes, hypomanic episodes, mixed states, and depression, it doesn't have to be so cut and dry, and there is almost never a pattern to it.
I don't know if they are common together or not. I do know that usually one illness will also come along with another illness, (co-morbid or however it is spelled.) Like bipolar and schizoaffective disorder. Or bipolar and OCD. Stuff like that. It could be possible and I would ask your doctor.