Sounds like you're getting sick. I notice, while cannabis usually helps in these situations, using it when I'm sick usually makes me a bit more uncomfortable. If I'm not sick, but I have a stomach ache for some reason, it definitely helps and never fails. When I'm sick, it's usually a whole different story.

EDIT: I guess what I'm trying to say is: use it when you feel it's appropriate. You'll learn when it helps you and when it doesn't. If it hurts in the situation of you being sick, it won't hurt too much. Just make sure you don't over-do it.

Also, mixing strains isn't like mixing drinks. You won't get sick from it.