You've gotten some interesting answers so far (LOL). Let's try to get to your problem.
Singing through your nose is a placement issue again. Retrain your focus. Do you sing through your nose with particular vowels or notes? Next time you sing try this before singing.
1st of all, I hope you are not cheating yourself by not vocalizing your whole range, and that you are properly using diaphragmatic breathing. If not, google the term and getting good breathing technique down. NOW, lets try using AH. No, I don't want you to sing specific notes, I just want you to sigh on the AH vowel.. Go from the top of your range to the bottom sliding your voice from a high pitch to a low pitch. Now when you do this, do you feel pressure in your nasal area? Try it again and use this alliteration. Think of bringing all your energy to the bottom of your gut (now this doesn't work for all problems, just for those who have placement problems in the head). Try it again. Keep practicing this until your focus feels like it has changed from the upper part of your body to the bottom part of your body. NOW add vocals. Think openess all over the body. Sing on the vowel ah, with slightly fast movement through the scales. Keep thinking "bottom of your gut". Pretend all that air is going down into your gut while you sing, instead of up into your face. When you feel yourself getting nasal, think of placing that nasal energy into a different place, and if you think of the abdomen area, the sound will sound full instead of nasal. Also, try deep breathing exercises. When you breathe out, pretend the air is traveling down into your body instead of out of the body. This will reverse the way you focus. If you focus your resonance away from your face, the unpleasant nasal quality will disappear. If you need more help, you can add detail to your question and I will try to aid you the best I can to your particular needs. Good luck to you and keep singing!