Starbucks benefits package is 6 weeks paid time off, and another 6 weeks unpaid where you can use sick and vacation time. Starbucks doesn't do intermittent leave unless you have a corporate job. The only way to get a consistent schedule is to change your availability.

The reality is that most managers are more concerned with staffing their stores than giving you a convenient schedule. I'd try to have another conversation with the SM, or maybe take the rest of your unpaid time off and use up your sick and vacation time.