It could be PIH, it could be the beginning of pre-e, it could be that you are a chronic hypertensive unmasked by pregnancy. The diagnostic criteria for preeclampsia is 2 readings of 140/90 or over, and 300 mg of protein in a 24 hour urine. At 280 mg, you aren't far from that, though it can fluctuate and if you did another 24 hr, it might be lower next time.
What it isn't, unfortunately, is caused by your weight or blood volume. If that were the case, most women would have high bp in pregnancy. I weighed 20 lbs more starting my pregnancy with DS, which was healthy, vs. my nightmare pregnancy with dd.
I'm glad they are watching you closely. In your shoes, I'd be watching my blood pressure at home too, if you aren't already.
Some women can limp along on bp meds and bedrest for a long time/until delivery without too much drama, other women can limp along for awhile and then suddenly get worse. What you are experiencing sounds pretty typical in terms of this forum, though.
Sorry you had to find this website but welcome!
Me (29) DH (30)
#1-Olivia Caetlyn-9-28-09-9-28-09, 23+2 wks, emergency classic c-section, class I HELLP, IUGR
#2- Lucas Oliver (rainbow baby)- April 2011, 36+2 wks, HELLP and pre-e free! (lovenox and LDA pregnancy)
#3-Matthew, late October 2012...mostly normal, 37 wks, (lovenox and LDA again)
My blog: http://www.butterflies-and-rainbows.blogspot.com/