I brewed my second batch yesterday and when I got ready to add my yeast I couldn't find it. Looked all over and I don't know what could have happened to it. Anyway I closed up my carboy and bought some new yeast today on the way home from work, but when I go to add it, the airlock was already bubbling and there is foam at the top of the carboy. I sanitized everything properly yesterday but I can't imagine what is making the bubbles except an infection. Any ideas?