I would seriously consider getting a second opinion w. a doc that will be there for you...this is some serious stuff and needs to be taken care of if you are on antenolol at only 50 mg. per day and your blood pressure is spiking like this that is just crazy...you need to get proactive with this one becaue your whole life could depend on it and hopefully your doc has you on an aspirin a day at the very least with this....i know my sister has borderline high blood pressure and she takes a 50 mg in the morning and one at nite...so what is their issue.....they need to help you out on this one...don't stop until you get the answers you need.....
As erijon correctly states, the white coat syndrome can cause problems but so too can an anxious person who seems to be quite stressed for different reasons throughout the day. To get blood pressure normal for an anxious person is very difficult as you can imagine. They could bombard you with beta blockers and ace inhibitors, then things will looks great. However, when a moment arrives when you do finally relax, it will of course plummet. So I guess the first thing to ask, are you generally anxious and stressed out? Have you recently had some worry in your life to deal with? It's always best to start with the absolute simple things before looking for the worse case scenarios. The first thing my Doctor says to me when my BP is a bit high is "ok, what are you worried about".
First off, don't take multiple readings at any given times, once per day, maybe twice. It is common knowledge that taking readings one after another will trigger an anxiety response that will increase your blood pressure. Also, don't EVER use drug store machines, they are not accurate due to over use and poor maintenance.
I had very high levels when mine was detected, mine is mostly due to white coat syndrome which means I test very high at the doctor's office yet my 90 day ave at home is only 110/67. The drug he put you on is a beta blocker designed to slow your heart rate. By doing so your heart works less hard and reduces your BP. Exercise will definitely lower your BP, but it needs to be more than just being active. It requires 30-60 mins per day, most days of the week maintaining an average heart rate of 75% to 85% of your max predicted heart rate (220 - age). The Atenol is not used to bring people back from the brink or prevent heart attacks no is it a vasodilator, only to lower your heart rate and help correct irregular heart rhythms by blocking specific receptors in the electrical system of your heart.
I'm sure you'll be fine until you see your doctor but seek help if you start to experience stroke symptoms. Other than that, relax, only take your BP once per day in the left arm, log it and take it easy.
Hope this helps,
Jon