I gained weight i took yeast infection pill and am sad and stressed can all this delay my period?

Absolutely: Although the yeast infection pill will not delay your period, the stress and sadness can certainly do this. Stress is a very common cause for delayed or abnormal menstrual cycles. Some women's systems are much more vulnerable to these changes in periods- some only need minor stress to upset things. It sounds like you would benefit from counseling re your stress and sadness. Please get some help.