Yeast infection can be sexually transmitted through oral-genital sexual contact. Other causes include prolonged antibiotic use, uncontrolled diabetes
You need an aggressive therapy that can be maintained to treat it completely. Smoking
doesn't cause yeast infection but it can delay the treatment as smoking lowers the immune capacity and this leads to persistence of yeast infection.
You must try to quit smoking and get rid of depression
These tips will help you quit smoking: http://med50.blogspot.com/2010/11/how-to-quit-smoking.html