Are you taking any other medications? Was the dosage of any other medication changed by your psychiatrist as you were started on Lamictal?
Also as medications are being adjusted the symptoms of what they are treating can return until they are at a working dose. Cognitive confusion and some of the other changes you describe can occur when starting Lamictal and generally get better with time but it would be essential to update your psychiatrist about this. They can tell you what to do within their clinical discretion.
I have taken lamictal for 4 years, 400mg per day, and it has never had that effect on me. But hey,,everyone is different and reacts differently to medicine.
My titration was slow, reaching to 200mg. All along the way I had bad side effects that did not go away with time. We tapered back down and the side effects are almost gone. We have one more taper, to a dose of 125mg. Our bodies really do react diff to diff drugs. Some more sensitive than others. Sometimes very small doses work for people. I don't know if you felt better and had no side effects on 25mg and everything changed at 50mg. If you were all around better on 25mg, your dr may just keep you at that. I'm not a dr of course but it makes logic sense to me if in fact it worked at the lower dose. As ILADVOCATE said, talking to your psyc dr is the best thing you can do. With everything you are experiencing right now I would call him today, tell him what's happening and he will advise you what to do. These psyc meds can often times take a while to work out. Often, side effects do go away with a little time, it just depends on the person.