hey thapap I just met the immigration counceling in my college and asked abt your question. you can get as many as OPT in life but you have to upgrade your degree. like if you do masters, you have one year OPT and if you go for phd after OPT in masters, you will get 1 more year OPT after PhD. but if you get OPT for masters and after you change your major to masters then in that case you dont get OPT ( in same level, it is one in life time) I guess it will help you