When I Smile, my Facial Expression Look Like I Am Crying. What Can Be Done?

I would need to see photographs to give you an answer to the problem you are describing. Otherwise it is a guess.

Firstly, it is essential that you get a consultation to properly evaluate your problem.
If that is not possible , a photograph would be helpful. Nonetheless, there are several nonsurgical options to helping certain aspect of your smiles- particularly the corners of the lips. These include neurotoxins , fillers, and lasers. Neurotoxins can help lift the corners of the mouth a little and stop a person from pursing his/her lips. This also lessens the upper lip wrinkles. Fillers can help the smile in multiple ways , including lifting the corner of the lips. Lasers can lessen/ remove the upper lip wrinkles, seemingly enlarge the upper lip, and lift the corner of the lip a little bit. Good luck to you.

It is very difficult to answer this question without evaluating you in consultation or seeing any photographs.  That being said, smile expressions that appear as if one is crying may have to do with certain dynamic lines (wrinkles from movement of facial muscles) created by making certain facial expressions.  If that is the case, treatments with injectable neurotoxins may help to relax these lines, allowing one to smile without appearing sad.  I recommend you consult with a board-certified dermatologist or facial plastic surgeon for an evaluation and discussion of treatment options. 

  Without photos, I'm not sure exactly what you mean.  Are the cheeks flat?  Are the nasolabial folds full?  Is there excess fat on the face that shifts when you smile?  Is there loose muscle and skin on the face?  IMHO it's paramount to understand and follow the proper aesthetics of facial beauty for the creation of a naturally, more attractive face.