I did the same thing-twice- and it took years for my metabolism to resume to being normal.
Now, that my metabolism is normal (amen) I am careful to steer clear of quick and easy solutions. I have read what is the "conventional wisdom" regarding how many calories a person needs based on height, weight and activity level but again if you have been dieting a long time, your metabolism may have become accustomed to "operating" on a lot less so all of that may be meaningless to you.
Instead, I try to be honest with myself with how much I do need vs how much I want. I try to follow the "one fist only" rule, read labels and follow the package guidelines for one serving (not three or four) and really pay attention to when I am full or even if I am hungry at all. Of course, it goes without saying, that healthy eating involves following the basic food groups and trying to aim for acheiving a balance among all of them (eat your veggies like we were once told).
Finally, I do not include exercise in as a means to aid me in weight lose. I have found that it messes with my head. 1) I feel that I can make bad choices since I have the "pain threshold" to tolerate hours exercising to "supposedly" work it off 2) that being hyper active is no substitute for healthy eating 3) lack of being active did not get me obese in the first place---overeating large amounts of food did so if that is the root cause then that is where I should start. Now, I exercise because it will keep me feeling limber and be "insurance" against being accident prone because I have tight stiff under worked muscles!
How many calories do I have per day: between 1200-2000. It depends on my hunger level.
I am learning to trust my body and what it needs.