Just keep walking, its such an easy exercise and many people can do it and it works wonders. Good luck.
Walking is a solitary "excuse-proof" exercise. You can't use the excuse that your tennis partner didn't make it or that it's too cold to play or that it's raining, etc. Walking can be done anywhere, anytime and in any weather. Actually it can be miserable walking in the rain but there are walking alternatives even to that. I have a treadmill for lousy days. At work (I walk at noontime as well), there is an indoor shopping mall where I can go on rainy days and get a quick three miles in with no problem. I simply walk around the perimeter of the mall on both levels, making sure that I also walk the perimeter of the anchor stores. I have it worked out where I walk exactly a mile on each level, so I do the bottom level, walk to the top level and do that and then do one more lap on the bottom level before going to my car. Just about exactly three miles.
To break up the monotony, I take "road trips" every weekend to someplace new. Could be a state park, the beach, a town center or out on the country backroads. I've found dozens of good places for walking during this past summer. During the week, I stick to the same few routes but I now have an MP3 player that I carry with me so that I can discover new music or listen to a book on CD (easily converted to MP3). When I am on the treadmill, I watch DVDs. Currently I'm working my way through the "Civil War" documentary by Ken Burns.
It's also pretty much an "injury-free" exercise. I highly recommend it to those who need a long-term exercise programme that actually works.