Storage Memory Reporting High Usage, But Can't find Where.

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I've been using my phone for the past 7 months with no problems, no hard resets or anything. Now all of a sudden i notice it start to get a bit sluggish. So i check the memory to make sure theres enough allocated to programs and it shows that storage has taken over. Storage has 90.81MB allocated and 73.22 in use and only 31.23 allocated to programs and 19.5 in use. now im guessing this is the cause of the sluggishness but i cant for the life of me find where all this storage is being used. Is this a fault or do u think there are lots of hidden files eating my memory. Any help would be appreciated.
Many Thanks
Angharad