I'm sorry you're feeling down about your loss of creativity and cognitive abilities. It could be meds. It could be the illness. It very well could be both. Do talk to your psychiatrist about these concerns.

At this time, I feel pretty good cognitively. I can't complain. Going off or reducing a couple medications I used to be on (with my psychiatrist's direction), helped quite a bit. Not all bipolar medications have affected me much cognitively, though. My current mix is pretty friendly in that respect.

My creativity varies. I believe changes are mood-related, for me. Or sometimes I lose some creative abilities for some things, but gain them for others. For example, for about one full year I was writing almost daily in my blog. There I wrote serious articles, prose poetry, short stories, story series, and other things. I was driven. Then writer's block set in. Then I really got into cooking and baking and recipe creation. Then nothing creative happened. Then I became immersed in philosophical thinking. Then a break. Lately, I'm not doing any of the above, but I've found myself to be particularly entertaining to myself. I've been acting a little nutty lately, but I love it. I've also started enjoying music again.

When I compare my current self to the young me, who could achieve so much, I don't feel I'm lower in IQ. I do, however, have a much more difficult time creating the same output. I burn out much quicker. My stress tolerance is much lower. I bounce back from episodes slower. Actually, I am slower physically. Part of that could be age and sedating meds. When I was young, I leaned heavily in the hypomanic/manic direction. That has shifted slightly with certain treatments. Nevertheless, I'm still speedier than my husband.

There were some years when I felt exactly like you describe. It changed/improved!