70 lbs. is amazing! I understand your frustration. Being stuck for 3 months does happen. I've seen quite a few people on here have very long plateaus. I think plateaus are a big part of why people give up. It sounds like you're not giving up...you're stepping it up by taking long walks. 3 miles a day is great! I think that might move things along again. Have you lost all that weight without working out? It's hard to know what you can do since you didn't say what you were doing. Do you count calories? As we lose weight, we need less and less calories in order to create a calorie deficit. You can create that deficit by either working out or eating less or both (which is ideal). Losing inches is a better indicator of success than pounds on the scale. If your pants are falling off of you, then you are actually losing weight! I used to know a woman who looked like she weighed 120 but she weighed 150. Really though, who cares about the scale? It really comes down to how you feel and how your clothes fit.
With regards to the blood pressure, it's hard to know....the body is so very complex. Have you increased your sodium intake? A lot of people (me included) will eat more processed foods because the calories are easy to gauge, but they are loaded with sodium. There are things that can be done to decrease blood pressure. Here's one article about that:
http://www.prevention.com/lowerblood...ly/index.shtml
Please don't be sad. You have SO much to be proud of! You will lose the weight....just keep plugging along. It may take longer than you had hoped, but it will happen. What's the alternative? Giving up and then gaining back the weight? I've done that. It's not fun and then you're back at square one.
Hang in there! You may just need to tweak things a bit. You may need to cut back on calories just a bit or maybe increase weight training (which helps you burn calories at rest).