Do you feel like you are saving the environment each time you use your reusable water bottle or coffee tumbler? According to Delish , you might not be cleaning it that well which defeats the purpose.
The seals that keeps the hot or cold in the cup is actually removable and it is recommended that it be cleaned regularly but a lot of people don't think to do that and because of that, bacteria gets trapped in the cup and grows, probably getting you sick! "That means with every sip of coffee, you're probably also drinking mold if your lid hasn't been properly cleaned."
OMG.... I think I just threw up! So gross!
It is the last thing we would think about while getting our coffee fix each day but it could also explain a lot of things like we aren't feeling good. My recommendation would be to either throw out the reusable cups you have had for a while, clean them very well or buy ones without the seal.