It's not just a side effect of some of the medications! It also depends on some concurring diagnoses. I, too, have great difficulty with concentration. It is due to my meds as well as my secondary diagnosis of anxiety. Anxiety in and of itself can cause concentration problems because of the way it effects the brain; it actually blocks your short term memory from picking up signals.
It cannot be fixed with more meds, but you might notice some alleviation when you stop certain meds. You have to ask yourself which is the lesser of two evils. I decided memory loss and inability to concentrate are the lesser of my problems. This is all information that I got from my psychiatrist when I addressed the problem with him.
I have learned to live with this as a side effect of BPD. Because of other underlying medical conditions, I cannot switch my meds, but you might be able to. Only your doctor can tell you and help you decide what is the best thing to do.
I hope this helps, and I hope that everything works out for your higher good.
Angel.
Word finding difficulties can be a side effect of some medications used for bipolar. Would you mind sharing what your current meds are?