It's my job

The low I've hit recently I'm pretty sure is job related. I posted about on here a few times - I was transferred and promoted back in January. The job is great, but exhausting and overwhelming at times. When I first started, I was managing a small staff (5 regular staff, 2 ft and 3 pt, plus 2 seasonal staff members) Shortly after I started the staff size dropped by 2 -  one of the ft staff got a transfer/promotion, and one left for a better job. As the supervisor, I was expected to cover all the empty shifts - sometimes as much as 50-60 plus hours a week, plus I have a part time job on the side that I work maybe 10-15 hours a week at. Even with us hiring new people, they are obviously not the same as fully trained staff. I doubt myself alot and often think I am not cut out to be a supervisor. Yesterday, I got a bonus day off because one of the staff offered to take my shift. I was so relived and happy. Then I got a text from a seasonal employee about her not coming back when she thought. it was supposed to be this weekend, now its not until June 20th. I have to cover the weekend shifts and re do a bulk of the June schedule, which I just finished. I literally started crying as soon as I read the email. It's like this all the time. Staff trying to get out of shifts, staff giving me late notice for not coming in or time off requests days before. Older (in age) staff members often I feel look down on me because I'm young. We're working hard at communication but when the staff just decides to do the opposite of what I said its so frustrating. The new staff members are doing well though, so I'm trying my best to hang on with the hope once they are fully trained my job will be easier. I feel like I've given this job so much of myself and I can't keep up. I just sucks because I actually love the work, and enjoy my staff as people, I'm just so burnt out.