The acid is carboxilic acid and thats supposed to be there because that is basically the 'Ester' one of the carboxilic acids is called enanthoic acid hence the name "Enanthate".
so this is nothing out of the ordinary and not to worry about it, however some people do react to it and they get sore and can sometimes experience flu like symptoms, this is your body's own natural response.
Your body reacts this way because you inject a substance that irritates the muscle and your body responds exactly like it would if you had a virus, so it cranks up its temperature to slow the progress of a invading virus or bacteria.
You could switch to cyp and this could solve the problem, this would also explain why your friend had no soreness from your Test E and you did, you just may be sensitive to the carboxilic acid ie: "enanthoic acid"