It's hard to say what could be causing it. I have always been underweight until recently and my blood pressure was 139/80 when I would go to the doctor. They said it was normal at the time but now that is considered high. I even had that blood pressure reading when I was 105 lbs. So weight is not always the cause. I now just happen to take migraine headache medication that is also a medication for high blood pressure called Inderal and it's in a more normal range so I feel better about it. I bought a high rated blood pressure monitor for home use and it matches what those drug store machines say. One thing I notice though is if I take it and then wait 10 or 15 minutes and take it again while sitting the entire time it goes down quite a bit. Today I took it and it was 122/85 and then 10 minutes later it was 105/83. So just the thought of taking your blood pressure and being worried about it can make the top number go up. It would be worth your while to get a home one. The one I have is called "Reli On" digital blood pressure monitor. I bought it at Walmart. It was not cheep I think I paid about $50 for it. Can't remember for sure though. It is the top rated one for home. Whenever I do the ones in the drug store my top number is always higher. If I actually take the time to relax for 5 minutes and do the drug store one again it goes down dramatically. Stress or nervousness make the top number go up. The bottom number is not effected by stress.