It will never just "become enjoyable". What may happen, if you open your mind to it, is you might realize that the discomfort you feel (which is different from pain! if you feel a lot of pain, get it checked out) is just a question from your body. It's asking you, do I really need to do this? Because animals have evolved to conserve energy whenever possible. If you can learn to mentally answer your body, yes, this is something we need to do on a regular basis, you'll learn to move past the agonizing over discomfiture. With time, you'll realize discomfort isn't a useful factor when it comes to exercise (although, again, pain is). As you discount it towards zero, you'll be able to focus on other things when you exercise (how's my body doing? what's my effort level? am I going faster than yesterday? what about that project at work? what's the meaning of life?). It may start to help you think, and you'll start to improve (that hill used to be tough, but now it's a piece of cake!). With time, you may look forward to exercising.
It's a process you need to work at, but it will enrich your life in so many ways if you can get past that tricky mental hurdle. I truly hope you do!