Baby always wants to go back to sleep?

Regs

She will nap for about 30mins to an hour, but no matter how long shes asleep for, she will wake up and rub her eyes or yawn and squirm until she cries unless I help her get back to sleep. Then she does another nap length sleep and wakes up the same way. I eventually just get her up and let her have a grizzle and then keep her up til her next nap but why is she always so tired???