If I understand the dates etc its only had a week of warm conditioning since kegging, right ? May be a bit soon to say but if it is truly flat then you may have a leaky seal around the lid - kegs can be a bit temperamental. I have a couple of King Kegs but from what I have read, the budget kegs are especially prone to leaky lids due to the seal design.
Has it been stored at 18-20°C so secondary ferment can get going ?