Why is my steering wheel jerking?

I got an alignment done abut a month ago but for the pat week I've noticed that the car jerks from left to right slightly. Is this something related to the alignment or is it something separate. Maybe a loose connection somewhere in the steering shaft? I'll be driving straight and then the car just kinda does a quick one to the left and I need to correct it then it does the same for the other direction. I notice this at higher speeds 55mph+. Any input would be great thanks!