This is why I inject weekly.
I heard weird things happening to people sometimes at the end of 2-3 week cycle, because some people have systems that process testosterone faster.
I've heard that administering weekly can help avoid testosterone reaching its decay time in your body.
I'm sort of wondering if you had a hysterectomy yet - because the ovaries have a high concentration of estrogen.
If you have ovaries and you are infertile by this point, then that could be why you're experiencing hot flashes - kind of like going through menopause.
Also, if you don't have ovaries by this point, then I assume having a low amount of any hormones in your body could attribute as to why you feel really strange at the end of your three week cycle.
I'm honestly just guessing most of this though and you are better off seeing a doctor (as several other people said) to be sure.