Almost certainly accutane-related. Not only is the drug neurotoxic (used in higher doses to treat brain tumors among others), but it also messes with neurotransmitter methylation. Less methylation = different behavior, in your case, amplified obsessions. Fortunately these side effects are temporary, and once the drug is discontinued methylation resumes as normal. Neuron regrowth has also been documented in extreme cases where the individual suffered from quite severe central neuronal atrophy. So I would not worry.
Eat plenty of protein, especially eggs, dairy, and liver, and get lots of fat and cholesterol for your brain.