Struggling with Mental Health: Seeking Support

Hey guys! I've been treated for ADD/ADHD, anxiety and depression for the last 20 years. All legitimate diagnosises...however, it seems that the older I get the more I'm finding myself in somewhat cyclic slumps that seem to grow worse over time. they're debilitating, and for no real reason. I can't seem to keep up with relationships of any sort, even with family- who I absolutely adore. My thoughts go from regular to dark for no apparent reason, making me question my sanity most of the time. I'm always aware of my down spirals, I just can't pull myself out of them. More and more I'm starting to think that the doctors have overlooked a diagnosis, possibly for bipolar 2? I'm just looking for anybody who is or has gone through the same thing....this is no way to live.