Thank you all for your advice and Sorry for my late response..
I checked the lens in my home as the seller did but as I am not professional I couldn't see any fungus. My eyesight is not good for this kind of things.
So I went to the dealer yesterday Tuesday morning and told them to check my lens for so called fungus. As I have the warranties for the camera and the kit lens, I have to leave my camera and lens at the dealer service center for tesing. They asked me to pick them up on Friday. I asked the dealer to check the camera too because I found a small dust on the CCD sensor. (As first I have only fungus inside the lens. But I found a small dust on the CCD sensor when I was taking the pictures after I cameback from the seller on Monday night.)
The dealer call me this evening and informed me that the camera CCD dust problem is under warranty and I don't need to pay anything. But the warranty does not cover for the fungus inside the lens. The dealer asked me whether I wish to clean the fungus and it will cost me 120 US $. But I need to wait 2 weeks to get the lens back as they need to order the spare parts from the Nikon.
What can I do? So I am thinking that whether I should agree to clean the lens or not.
As I said before I wish to buy a 70-300 mm VR or 18-200mm VR.
So now I have 4 choices:
1) repair the lens and buy a new 70-300mm VR (about 100 $ + 650$ = 750 $)
2) buy a new 18-200 mm VR and forget the 18-135 kit lens (about 800 $)
3) buy a new 70-300 mmm VR and forget the 18-135mm kits lens and use with my 50mm/f1.8 for the below 70mm shots. (about 650 $)
4) forget about repairing the kits lens and use it until it dies. (probably it will be lasting for one year) (no cost until now)
Please give me some advice for above selections.
And one more question-
Will the fungus spread to the CCD sensor and the other lens that I have if I won't clean the fungus?
Oh I need to tell you that I am now staying in Thailand and it has a tropical weather so it might be the reason to get the fungus so early (within 2 months). But I live in Bangkok not in the other provinces and travelled only to one beach since I bought the camera in December.