Clingy stage

My little boy is 2 years old and I've found this stage really challenging. This week has been particularly difficult. I know that toddlers go through a clingy stage but he's not clingy for me. I am currently doing a full time degree. I took 2 years out when I found out I was pregnant and I've got one more year left. I'm also not with my sons dad so I rely on lots of family support (which I do have). Even though our home is in Cornwall because my degree is in Plymouth we decided to move in with my parents until I finish my degree as its easy to get in to university from there. I spend 5 and a half days in Devon (although I have uni 3 days when my son is in nursery) and then I go down to Falmouth to work 1 and a half days a week as my business is down there. So I actually only get 4 evenings and 2 days with him a week. It's really hard but I don't have a choice and I'm doing this all for him, to have a career to support us. I'm also self funding the degree and only working 10 hours a week so there is a lot of financial strain. My parents have been amazing for the last 2 years and I wouldn't be able to keep studying without their help. My son has built an incredible bond with them which is lovely to see. I guess as my mum is there all the time, my son sees her as the person he feels most safe with. He knows who mummy is but I don't think he understands the difference between grannie and mummy. This week he won't let me do anything. He only wants grannie and is always crying and calling for her. He won't co sleep with me, he won't let me settle with him in his cot. He just wants her all the time. I try not to let it effect me but it really hurts. Of course I know it's not personal and I'm lucky to have people that he feels so happy with but I'm his mummy and he doesn't want me😪 I always feel so guilty that I can't spend more time with him and that I have to work away every week but I worry about our bond. In a year we will be moving away and having our own life but I'm so worried how he will respond to the change. Just feeling hurt right now😪