I've been taking Doxycycline for the past 2 weeks for mild acne, and since then I've gained 10 lbs?? It does not list weight gain as a side effect of the drug, but I've looked up stuff online about it, and I'm seeing that a lot of people had the same problem. They say they gained 10-20 lbs while on it.

What is going on? Why does this happen?