My sense of purpose comes from self improvement (learning new skills, improving skills I already know), it has very little to do with my work anymore. I believe it's dangerous to tie your self worth and purpose to your job. Working in the corporate/private sector will only drain you when you realize the company you work for treats you like a resource rather than a human being. So my advice is find purpose outside of your work, and use your work as a means to fund your needs/hobbies/interest, rather than your purpose for existing.