I learned in a online article that when you try to forget about some bad experiences you forget also some of the other memories/information from your brain which is important to you but they occurred at the same time which you are trying to forget about. So this explains why I feel like forgetting so many important work related formulas and programming knowledge that I learned during my Ph.D. I had my gf then for the 5 years of Ph.D, who broke up with me last month. So I always try to ignore her thoughts and I am also keeping forgetting usual stuff of my work that was easy as pen and paper to me. Hmm.. I should not force myself to forget about my ex.. its a loss at a bigger scale.