Returning to work, HIGHLY stressed!!

Hi. Just wanting to ask fellow mums a question. I've been a stay at home mum for the most part of 11 years, I've had a Few jobs that were good where I could be at home and take my kids to sporting activities on weekends when I had my children. Now I'm in a full time role 9-5 Tuesday to Saturday and I'm finding it so hard, I feel so guilty that I can't be there for them in the afternoons after school and I only get to spend time with them on the Sunday as they are at their dads on a fortnightly weekend.. I miss them terribly when I'm at work which is weird because they are all at school so I'm used to not being around them 8.30-2.30.. I seriously have cried at work.. I'm even missing my partner while I'm at work. I have no idea what is going on with me at all