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Yes i have a feeling it is sun burn as well, because the side facing the sun (through the window) is green, but the side that was away, the branches have turned yellow and so have the leaves. How can i solve this sun burn problem ?? Is it going to go away ? And will it affect my tree in the long run ?

No don't do that, if its been in the same spot for months and hasn't been sprayed with anything, it isnt sunburn, and it needs light. hmmmmm Salt burn? Did you recently fertilize it with something new?

Spreading the Mulch A 2- to 3-inch layer of mulch spread around the base of each citrus tree is enough to hold in moisture, regulate the soil temperature and prevent weed germination and growth. The University of California San Diego Cooperative Extension recommends maintaining this layer constantly throughout the year. Preventing Root Rot A common cause of root rot is lack of oxygen exposure, which can occur if the mulch is spread too close to the citrus tree’s trunk. To help eliminate the threat of root rot, spread the organic mulch at least six to 12 inches away from the citrus tree’s trunk. This prevents excessive moisture retention around the roots and allows for proper air circulation.