Hey sarie - to balance your PH you have to eat the right foods - alkaline foods (fruits/veggies, raw oils, raw nuts/seeds). If you're worried about your weight, an avocado a day, a handful of nuts or seeds, and a tablespoon or raw oil on a salad or on steamed veggies will help you from dipping too low (I've been there too, it's really hard at first to keep weight on when you become vegan and eat alkaline foods, but consuming the foods I mentioned above will definitely help). Also, eat lots of fruit - it's very cleansing and is alkaline, and contains lots of energy for your body.
Juicing is also GREAT for alkalising your PH - get a juicer if you don't have one, and juice a pound of carrots a day, and throw in a few oranges and a lemon as a tasy alkalising and detoxing drink (juice about 4 stalks of Celery too, it doesn't taste great, but adding some fruit with it helps to sweeten it). It must be drank every day though to get the benefits. Jucing can be annoying at first, but now I find my body absolutely craves the juice. My juicer broke earlier this month and it was in the repari shop a week (thank goodness for warrenties lol) and when I finally got it back I juiced for two days straight. It;s all my body wanted, I felt so under-nouished and weak without juice everyday.