Wyeast 1968 is a highly flocculant strain, which means it drops out of suspension quickly.
There are pros and cons to this characteristic. On the plus side, it means star-bright beer without filtration or fining. On the minus, it often means it settles out before an appropriate terminal gravity is reached.
Post your recipe. We can guesstimate your OG from the grist. If you haven't bought an hydrometer yet, do so at once and take a gravity reading. Post that information also. Post the ambient temperature of the room where you're fermenting.
In the meantime, do nothing except gently rouse the yeast. If the beer is in a bucket, clean and sanitize a long, stainless-steel serving spoon and swirl the beer until you get clumps of yeast rising off the bottom and well mixed (avoid touching the sides and/or bottom of the plastic pail or you'll scratch and ruin it). If the beer is in a carboy, GENTLY rock the carboy to set up currents which will resuspend the yeast flocs. Note: Take your gravity
before rousing.
Highly flocculant yeasts, like Wyeast 1968 and 1187 (Ringwood), should be slightly overpitched for best results. You, unfortunately, underpitched. You probably should have pitched more than twice the amount of yeast you pitched with that one XL smack-pack. (See the
HBT Wiki article I wrote on pitching rates.)
That's why you had a sluggish ferment. It's probably still working, albeit slowly; it'll continue to work for a time.
BUT - do not pitch more yeast until we say so.
Cheers,
Bob