I cannot tell you whether it is normal for your level of use, but it is perfectly normal to happen at some time.
What you describe sounds like common clotting of the feathers due to the influence of moisture and pressure in use over time. When you detect this very early, shaking and crushing the bag may be enough to restore loft. If this is not the case, you can wash the bag with special detergent. Do not use normal detergent or softener, only detergent clearly labeled to be used on down bags! If you use a machine for washing it, do not use spinning! After washing, either dry it at normal temperatures while shaking the bag very often or use a tumble-dryer. The first way is optimal, but very laborious. For tumble-drying, you should put the bag in a cloth-bag together with several tennis balls. This will make sure that the feathers do not clot when drying. Dry it on low heat.
While it is necessary to wash the bag, when clotting gets persistent, and it thus prolongs the time you can use it, still do not overdo it. After too many times of washing the performance of the sleeping bag decreases.
Edit concerning top-loading washing machines:
Do not use top-loading washing machines, the agitator can damage your sleeping bag.
Maybe the delicate settingfixes the problem by locking the agitator in place, but check that first.
Thanks to requiem for the note, I was not accustomed to the concept of top-loading waching machines (not common in switzerland).