Ramadan:Muslim sis please help me out? Plz open my question its urgent.?

Okey here is a problem, m going to choaching classes where i have to sit for six hours( they offer 30 minutes of break) and that too with boys and girls both. The problem is i wear niqab,though i dnt hide my face, its realy very difficult for me to sit for six hours continously in niqab that too in hot days of summer in India, they dnt have air condition facility. I want to do purdah coz i do it by my will, but the inconvinient weather makes me very uncomfortable , and i m unable to concentrate on my studies. Can u plz suggest me some comfortable alternative, where i can do purdah and whil being comfortable. Plz help me out.