Sir I'm 19 Year Old Men...sir My Problem Is I

Sir I'm 19 year old Men...sir my problem is I don't know my way of thinking about my self confidence....when I'm with my frnds my confidence level is high....and but when I saw girls I think she is not interested in u or wht u have so she look at you at that time I don't know wht I do with type of thinking...please sir help me!!!