D.M.
First, take a deep breath and relax for just a second. It's going to be okay.
My son has struggled with seperation anxiety on and off, since he was about 13 mos. and I went back to work part-time. I'm a single Mom, and I depend on my parents a lot for childcare and help with my son. For a while, he wouldn't let me out of his sight and would fuss and be angry for sometime after I left him for anything!! It broke my heart, but something I learned is that my stressing about it made it worse. He could sense my own anxiety over the situation and that made it harder for him. He could tell Mommy didn't want to leave him, and that hurt. Eventually, I took him out of school and even his teachers agreed it was best...but, he never got super happy about being at school.
What I did at my Mom's suggestion is I worked on creating time that was special just for me and my son. I work full-time now and he visits his Dad every morning for four hours and then is with Grandma until I get home from work. When I get home, we go upstairs and get into 'comfy clothes' together, and either go outside and garden for about 30 minutes or read and play upstairs in his room for 30 minutes. Then, he helps me cook dinner. But, it's just us and he knows he's going to get his 'just us' time. On the weekends we have a routine on Sundays where we go get donut holes and grocery shop together, he helps me with putting stuff in the cart, etc. Every other Saturday I try to plan a big adventure for 'us', either the zoo or park or beach, something that doesn't require a lot of money but that allows us to share in some educational bonding time.
Your son is just trying to figure out where he fits in the routine. I saw my son be confused and frustrated and start doing things that were totally not in his character. Don't worry, he knows you love him and this is just his way of trying to make sure he gets his 'Mommy' time. Try to create a pattern of 'Mommy and son' time that allows him to have something to look forward to and antcipate during his day.
If he's happy in school and does well, then I would talk to his teachers before you make the move to change that. You don't want to disrupt his routine too much, as that could make the clingyness worse.
I felt so lost until I sat down and asked for help, and it's good when we finally do!!! You're working really hard to provide a future for your son and that is awesome! Just try to give yourself a break, and enjoy the right now too.
Good luck and keep doing your best!!