Only 3 is good. You could also say: You don't know what I've been going through

You don't know what I've be through in the last few days.

You don't know what I've be through in the last few days.

Hi there Sinem, Some interesting prepositions here! I agree with David, only the last sentence makes sense in this sentence and it is even better with the sentence he's given you of "you don't know what I've been through over the last few days". 'To be in' means to be inside something or other phrases we use in for, like to be in a musical. "I've been in school over the last two days"' To be over something can mean you don't care about it any more "I'm over it" and "to have been over" something means to have revised it, to have looked at it, to have covered it. "I've been over all of chapter 2 with my students but they still don't understand any of it!" And "to have been through" something means the same as to "go through" something. It means to work through, to push past, to conquer, to endure, to experience. Eg. "I've been through so much recently. I just want to go to bed and sleep." And then "over the last two days" means during the last two days. You could also say "over the course of the last few days" Hope this information has been helpful and your head isn't aching too much from all those prepositions! Best wishes, Katherine

3rd one make more sense. In case of 1st 2, readers wont understand what it means. It can be, 'You don't know what I've been doing these past two days."