Oil problem!! Help asap!!!

so my 07 lgt goes through oil like beer at a bar. i put the car on jack stands and looked for leaking and found no leaks, drain plug and oil filter were both tight. but for some reason i need to keep filling the damn thing with oil once every three weeks or so.. it never gets completly empty only to the fill mark, but i should be able to go 3500 miles with out worrying about blowing up! so i was wondering if anyone knows of a solution before i take it to a local subaru dealer and pay $$$$$...

HELP PLEASE!!

you should be posting up in the 4th generation section for your lgt, this is the 3rd gen (99-04 legacy). about your issue, the oil is going somewhere so i would recheck carefully to make sure its not a head gasket. is your car over heating?