The family hamster is sick?

i fed her her usual blueberry and pea pod for a snack she also had walnut and a blackberry but she has had them before with no trouble. this was 4 days ago and the day after she had the snack she was shaky and couldnt open her eyes and sleeping all day. the next day she recovered and seemed more energetic even managed to shred toilet paper for her igloo she sleeps in. now 2 days later she is back to shaking when she walks and cant open her eyes , very lethargic. ( she ate some watermellon, but thats all ive seen her eat/drink). the vet said we could bring her in but last hamster cost 200 and he never found anything! do hamsters get colds or flus or is it maybe the walnuts?she is about 1.75 a white european hamster.