Tea making me sick??!!

I havent really been taking care of my body through clean eating and light exercise because Ive been sooo busy with kids and work. Well now my youngest is 11 months old so I want to try again.

I want to start by eliminating all sodas and alcoholic drinks and replacing them with tea (teabags not the leaf). I used to drink a lot back in the day especially plain green tea or green tea with fruit infusions.Now, whenever I take a few sips my tummy starts to ache and then heave and I become so nauseous that I stop immediately. I noticed this way back then and now its happening again.

What is happening? Am I making itto strong? Could it be the drops of lemon or lime that I squeeze into it first/ Is it because Im attempting to drink it on an empty stomach? What could be the cause?

Please,if there are any of you experiencing similar symptoms ,I'd like to know about the cause and cure.