I recommend having your hamster examined by a veterinarian.  The increase in weight may be due to a high fat diet--like milk and cheese, an illness, or possible pregnancy.  Was your hamster around a male hamster in the last few weeks?  Change in behavior-not letting you pet her--could be due to an illness or possibly pregnancy.
If she is pregnant it does not sound like she is on a balanced diet--good diet is important during pregnancy.
Your veterinarian will examine her for illness and can discuss proper husbandry of pregnant hamsters including how to care to the babies.

 Yes it sounds like she is pregnant make sure you give her some fresh fruit and this will keep her healthy and hydrated

 Well my hamster was pregnant 27 days ago and she would let me hold her ate normal and was medium so im pretty sure your hamsters pregnant if so she'll give birth probably at night