Tread on somebody’s heels
Definition 1 of 2
Pro Tip 1/3Implies Annoyance
Suggests that the person being followed may feel annoyed or harassed. 
Everywhere I went, I could feel her treading on my heels, and it was starting to irritate me.
Pro Tip 2/3Persistent Action
Indicates a continuous and relentless action by the person following. 
Even after I asked for privacy, they kept treading on my heels with more questions.
Pro Tip 3/3Not Literal
Used figuratively, it doesn't mean someone is physically stepping on another's heels. 
The new intern is hardworking, always treading on my heels, seeking approval.