Unsettled since starting nursery

Any advice is much needed My little girl is on week four of nursery ( does 5 full days 8:40-15:30) she is normally a happy little girl and is excited to learn new things, and meet new children, when she first started nursery it was a good first 2 weeks as she only done half days to settle in , but now she’s in full days it’s becoming a battle, lots of tears at drop off the minute she sees the school gates, saying her tummy hurts, so her teacher just takes her off us and take her in. It doesn’t matter who takes her in, if it’s me her Nan or auntie it’s still the same, but once she’s in the teachers say she’s fine after 10 minutes, but when it comes to picking her up, she will not speak to anyone and will just go into herself and bury her head, but it’s also happening on weekends aswell? I feel like there’s something going on but I can not put my finger on it, as she’s just gone dead quiet , very clingy, won’t go to her dad just wants me all the time, whenever i move shes getting upset, its really getting to me because i don't know what else i can do.