can you do an if statement after an if statement?

My BMR calculator isnt giving me the correct result, I know if I take out the if loop that checks the activity is the right answer but I can't find what needs to be changed

double doubleweight = Double.parseDouble(Weight);
double doubleage = Double.parseDouble(Age);
double doubleheight = Double.parseDouble(Height);

double BMRm, BMRf;
BMRm = 66 + (6.23 * doubleweight) + (12.7 * doubleheight) - (6.8 * doubleage);
BMRf = 655 + (4.35 * doubleweight) + (4.7 * doubleheight) - (4.7 * doubleage);

double bmr;
if ((null != Gender) && "Female".equals(Gender)){
bmr=BMRf;
}
else{
    bmr=BMRm;
}

if ("sed".equals(Activity)){
    bmr=(bmr*1.2);
}
else if("lightact".equals(Activity)){
    bmr=(bmr*1.375);
}
else if("modact".equals(Activity)){
    bmr=(bmr*1.55);
}
else if("vact".equals(Activity)){
    bmr=(bmr*1.725);
}
else{
    bmr=(bmr*1.9);
}