Why do they. . .

I was just wondering if it's normal in some cases for your bags to leak down? The thing is, they haven't been doing it until a day or so ago, and only the front leaks down. Also my tank leaks about 20-30 lbs overnight. Should I check and re-tighten all my fittings or what? It's been kinda cold here and I know that messes with stuff. Thanks for any help.