I struggle with BP issues all my last 2 preg and seem to be keeping them in control this time.
Have you checked out blueribbonbaby.org? (the brewer diet). I follow a kinda personalized version of this. Tons of people swear by it.
One of my big triggers seems to be not enough protein. My goal is 80-100 g of protein a day and I was doing good until the last 2 weeks, I just can't eat enough right now, so I am starting to eat high protein meal replacement bars (20 grams prot) as a snack to get enough. I can really tell the difference if I slack off.
Ca/Mg/Zn supplement is really important too. you want about 1000 mg of Ca, the Mg and Zn are also needed to complement it - the Mg is also really important in keeping BP down.
If I feel crappy or my BP is edging up I take a bath (at least 30 min) with a couple of cups of empsom salts dissolved in it. The combination of the water being absorbed and the Mg in the salts really helps.
WATER is really important. IF you are dehydrated AT ALL your BP will automatically go up. I drink prob close to a gallon of water/day. I often drink a midmorning "energy drink" of a big glass of water (quart jar) 2 packets of emergen-C and a couple scoops of an all natural powdered gater-aid mix. This seems to really help, esp when I am feeling thirsty (I get dehydrated very easily normally, so this may be more water then you usually drink).. I was reading something the other day (sorry can't remember what) but it recommended you take your weight in lbs, then drink that many OZ of water/day. I am a big person, so I don't drink quite this much, but I try to use it as my upper goal.
Sorry this go long, But I hope it helps.