from one of my favorite sites,
http://www.etymonline.com/s13etym.htm
suck - O.E. sucan, corresponding to L. sugere "to suck," from PIE root *sug-/*suk-, of imitative origin. Meaning "do felatio" is first recorded 1928. Slang sense of "be contemptible" first attested 1971 (the underlying notion is of fellatio). Suck eggs is from 1906. Suckling is early 13c.