I M 8 Month Pregnant.my Bp Was 140/100 So My

I m 8 month pregnant.my bp was 140/100 so my dr has rxed alphadopa 250 mg 3 times.still my bp was not controlled than dr asked me to take alphadopa 500 mg 3 times a day i hv bn taking three times from 2-3 days but still bp is not reduced.
Now dr has rxed lobet 100 mg once in the morning with alphadopa..and dr told me that if bp not gets controlled than we will hav to do preterm delivery..i m scared is it right treatmnt pls guide mam.