Hi Mohamed, If you are willing to go to that part of the country then I would suggest you to go in after February. Best season is the best to visit Sikkim that is from March to May. But you are planning to go recently then I think October-November is good because right now there must be all cloudy and you will hardly see the beautiful mountains. One more advice, try to visit north and East Sikkim too that includes Nathula Pass, Lachung, Lachen, Yumthang Valley and Gurudongmar Lake since those are the most beautiful places in Sikkim.
Hello Mohamed! Places like Gangtok and Darjeeling are blessed with extraordinary charm. In order to make your honeymoon trip a memorable one, its good to visit at these places during winters. To avoid crowd, plan your trip in the months like November, January and February.