With only 3 injections, even if you use Tren, you shouldn't be having any sides yet. I vote for the "anxiety" theory. Only your mind can produce such immediate physiological reactions! Even if you had tainted gear, it would take a week or so for any infection to show itself.
I've had "test flu" feelings before; that seems to last only a couple of hours. Also, I notice I get the sweats when I fail to keep my levels even. ( i.e. miss an injection) So your response might just be your bodies reaction to its changing hormonal climate and all will calm when you reach stasis.
I think (and hope) it's only your own anxiety at crossing over to the dark side. All should be well when you get more accustomed to your life choices.