Feeling Up and Down, and usually bad after NOT exercising

So, I’m 5’8″, 40 years old. I started at nearly 270lbs, now down to 238. I started with a diet the week of Christmas (seriously) and started exercising at the same time. I’m doing the Couch25K thing and I’m eating a lot of fruits, veggies, low protein, and almost completely avoiding carbs, and almost no added sugar at all.

Here’s the thing… when I exercise, I feel great. I feel great afterwards. I really had no idea I’d feel as well as I do given age and weight. I feel great the next day. Then by about day 3, I start to come undone. By day 4, I come completely a mess. On the day after exercise, after I eat, I feel great. But by day 4, I feel like my blood pressure surges when I eat, and my sugar levels seem to be up and down. I’m a mess. And I only feel better when I then exercise. It’s nice motivation, but I’m kinda sick of the ups and downs and the pressure it puts me under. My BP is like 120/80 on day after exercise. By day 4, it’s about 140/90.

Yes, I told my doctor. They did a complete series of blood tests, including glucose and a complete metabolic panel, and everything is normal. And like I said, what ever is “wrong” with me, running for 20 minutes seems to fix me for 48 hours. She knows all of this and once those blood tests came in fine, that was the end of things.

What’s going on? This is kinda getting to me and is sort of roller coaster. I used to drink maybe 12 beers/week, would eat pizza for dinner and lunch. Just an awful diet, soda, lots of sugar the whole nine yards. Although all my metabolic levels tested fine, is there some sort of adjustment I’m going through? This is exhausting.

I see my doctor again in 2 months to discuss how thing are going with exercise and diet. But in the meantime, what do I do? Please tell me my system will adjust and this will end at some point.