I am 31 years old and amh level 0.91 does this mean that it will be difficult for me to stay in pregnet or that i only have a little time left?

The AMH is a general indicator of the number of follicles (eggs) in your ovaries, which still number in the thousands, and has nothing to do with staying pregnant. Yours is somewhat low but is not predictive of menopause or fertility (which is dependent on multiple factors). Fertility steadily declines from about age 25, so, all things being equal, start a family when younger.