The fact that you do not feel the nausea underwater but only at the surface after the dive, suggests that it might be related to the pressure change during the ascent. The following suggestions of causes are roughly in the order I thought of them, i.e. most to least likely.
If you are having trouble equalising, or 'forcing' equalisations on the descent, this may indicate that you have also suffered a minor reverse bock during the ascent, which is affecting your sense of balance, producing dizziness. This should wear off with time, as the excess air escapes from your middle ear. Forcing equalisations can also damage your inner ear, but if this was the problem, the vertigo and nausea would not be temporary, but would continue long after the dive.
Remember that you should not be diving if you are congested (e.g. with a cold or allergy), and that you should equalise early and often during the descent, BEFORE the pressure becomes painful.
If you mean you are feeling like you need to throw up, this could indicate that you have swallowed air during the dive, or that you ate gassy food before you went diving--belching may help here. It might also indicate that your gear is not properly adjusted--perhaps you overtightened your BC cummerbund around your middle (remember, your suit will expand during the ascent, so a 'just right' adjustment underwater will become too tight after ascent).
Or you could be getting seasick. Ginger is supposed to help with this, or you can buy over-the-counter seasickness remedies, or acupressure bracelets.
Or the nausea might simply be psychological, a manifestation of the adrenalin rush, especially if you are slightly nervous about diving. Only you can say how likely this is.
There is a very remote possibility that you have suffered mild carbon monoxide poisoning from a bad air fill (e.g. if someone left a car with its engine running near the compressor intake), although in this case I would have expected the nausea to manifest underwater, and it would affect all the divers who had their cylinders filled at the same time as yours. The air would likely have tasted 'oily' too--although a newbie might assume this is normal (it isn't!).
As you are a relatively new diver, I am assuming that you are not doing excessively deep or long dives, so DCS is unlikely to be the cause of your nausea (and DCS has many other possible symptoms as well, such as numbness, paralysis, or pain--see your course manual).
However, if you are still concerned, or if the nausea does not dissipate with time, or you suffer any other symptoms, I would suggest you get in touch with the Divers Alert Network helpline (Non-Emergency Medical Questions: 1-800-446-2671 or 1-919-684-2948, Mon-Fri, 8:30am-5:00pm). They are better qualified to offer advice on SCUBA medicine than I am.