You have a great fermentation going on. The only issue is it is creating more CO2 than the S-lock can release (i.e., "bottle-neck.") During the first three days when ferms are this active, many brewers use a "blow-off" tube, which is often just 1-inch diameter tubing jammed into carboy and the other end is in a large volume of sanitizer. Once the major activity has passed, switch to a 3-piece airlock or your S-lock.
I've noticed quite a bit variance in different yeasts' likelihood to need a blow-off tube. Nottingham dry, for ex, usually has a one-inch krausen and has never been higher than that for me.