You most definitely can pursue a degree in computer science. And yes it will be hard work, but if you have passion and interest in computer science and/or technology then you will be happy you did. I am a big believer in individuals being well rounded and I love folks who have diversity in their backgrounds so I think it is great that you already have a degree in theatrical design. The creativity of this field will have a positive impact on your abilities in computer science.
Were you wanting to pursue a second undergraduate degree in CS or were you hoping to get a master's degree of some sort? Depending on your career interests and your educational goals you have many options. If you are hoping to do software development I think it would be best to pursue a second undergraduate degree in Computer Science. But you also have the option of taking undergraduate courses to fulfill prerequisites for graduate degrees. You will need to take mathematics, but depending on what area of development you may not need much past calculus. Your best bet for starters would be to identify a school or program that you are interested in and meet with an Academic Adviser. Find out about the programs they offer, the program requirements, and share with them your career goals. Then maybe take a class or two to test the water. For example you could take an entry level programming class or any entry level IT course that you are interested in. From there you can fine tune your goals and align them with a program that is best for you. And once you begin, don't forget that there are many support systems to help you be successful, so use them! It will get challenging but reach out to those support systems at home, at work, and at your school to overcome the challenges.
It definitely sounds like an exciting new adventure for you! I wish you the best and let me know if you have any follow up questions or if you need more specifics.
All the best,