What you have is common with DSLR. Your sensor has gotten some specks of dust on it so whatever you shoot tend to have the same specks on them in the same places of each photo. This is not a problem with the lens. Some of us do the cleaning initially with a blower brush to see if we can blow the specks of dust away. Set the mirror to lock in the lock position so you can look right inside the camera (once you have taken the lens off the body) you should be able to see the sensor at the back of the camera's interior. The idea is to use the blower ( take off the brush tip) and then squeeze the rubber ball to jet air inside the compart towards the sensor but don't touch the sensor with the tip of the blower or your finger.
This should dislodge dust that is not stuck to the sensor. You can check that by shooting a white plain wall and then look at the photo to try to spot if the dust is still there. Btw...set your f-stop to F8 to f16. This will sharpen the image so that it makes it easier to spot anything. Now if you have never done this before...well ...welcome to the club. We have to clean this every now and again. This is the most basic cleans you HAVE TO DO. No lens and camera in the world can avoid this.
For specks that can't be blown away because some how it has sticky stuff that glue itself tightly to the surface of the sensor's coating. You will need a more direct way to clean it. This require special cleaning kit and some strong nerve and delicate fingers. This is done by some of us who don't mind the risk of scratching the sensor's glass coating. You have to be very careful if you want to do this yourself then to send it to Nikon Service Centre, pay money and let them do it. If you have no confidence, send it on and pay the expert to do this.
The way to find out if your lens is dirty...just take about lens and shot a sample shot. If you still see the same specks in the same places...it is NOT your lens. The dust is in the sensor.
I can go on but I think you get the general idea and you can google tp get a lot more information on this dust problem beside the TONS of writings on this issue in CS if beginners just take the time to do a search.
http://www.clubsnap.com/forums/showthread.php?t=396889