Obviously not a doctor here, but if you have been to IP multiple times in this mental state you describe and the doctors did not diagnose you with bipolar during any of those IP stays, then either (A) you don't have bipolar, or (B) you may have intentionally or unintentionally withheld information from doctors that they would need in order to diagnose you with bipolar. But if you have had multiple "evaluations" in an IP setting and doctors STILL don't want to diagnose you with bipolar, I would personally think no to the Dx. I mean, I could be wrong, but if you have felt this way multiple times and each time they've said no to bipolar despite observing you in a controlled setting for days at a time, they must have their reasons? But if you are hiding things from them, then it's certainly possible you have bipolar and it's going unnoticed. So it depends on how open you've been with mental health professionals.

Also, there is such a thing as MDD w/ anxious features and MDD w/ psychotic features. And PTSD, as you say, can definitely mimic bipolar in a lot of ways.