I’ve been super lazy over the last year too… Too much time studying, not enough fun time. If running and things doesn’t do it for you, maybe you’re fitter than you know! I find swimming tires me out faster than biking or running, but that could be because I just splash around not going anywhere. The longer or harder you do any exercise for the more you’ll feel it! Maybe get a friend to do it with you and push each other a bit, or try mixing it up with different activities each day so it doesn’t get boring