Is it permissible to repeat the recitation of Al-Fatiha in a single rak'ah, or to increase the number of rak'ahs due to forgetfulness, especially when suffering from distraction and forgetting to complete the pillars (of prayer)?

Obsessive thoughts continue to plague you, and the only cure for them is to disregard them, ignore them, and pay them no mind. So, if you doubt whether you recited Al-Fatiha, assume that you have recited it and proceed with your prayer, and do not repeat its recitation. And if you doubt whether you are in the third or fourth rak'ah, estimate that you are in the fourth and do not perform an extra rak'ah.