Freud asks the question `what does suggestion mean?` He then
distinguishes between two forms of suggestion: a) internal & b) external.

Haas,Dictionary of Psychology and Psychiatry

"Fremdusuggestion" is used in Germany as opposed to "Autosuggestion", and I reckon any suggestion that doesn't come form one self (i.e. is "auto") must be, by default an "external" one - doesn't need extra mentioning.
If autosuggestion has been mentioned before, then you could just say "other suggestons" or "external influences"