This is my donor area (4000 grafts) after hair transplant. Is it good till now? Especially at the sides (Photo)

Your donor area will always look "thinner" proportionate to the number of hairs taken out after a FUE harvesting surgery.  The hairs will NOT grow back from the donor area (where it was taken).

Although there is no pre-op photo for comparison the donor area appears thin (probably from overharvesting),particularly the right side.

I am hoping there is considerable shock loss in this extraction donor. Because if this is actually all extraction you have been over harvested. Shock loss will return in about 3 months. The best way to correct this issue from a none experienced clinic is to decrease the density from the the most dense places and add that to your recipient and then get a scalp micro pigmentation to darken your donor. This is a great option and you will not look so thin in the donor.

Your donor area appears to be depleted. If you require further surgery it would have to be strip surgery or you should have been advised to have strip surgery in the first place. 

Sometimes  there may be such a early phase weak and  low density spots  in donor areas after FUE surgery,  but fortunatelly most are transient. İt may happen because of over harvesting or transient post traumatic shedding /shock loss. Any way it heals and hair regrow in 4-5 months of hair restoration surgery .

Thanks for submitting your photos. Based on them your donor site looks weak and over harvested. Please consult with your own doctor and ask him about his opinion.

With 4000 grafts and the see through donor area you have, the donor area seems depleted more than reasonable for your original donor density