Regardless of what the OG was, it's a safe bet that 1.030 is not a terminal FG. If this was an extract + steeping recipe then you can assume the OG was whatever the ingredients calculate out to. If it's a commercial kit then they may tell you what it should be in the instructions. I'd expect an oatmeal stout to have an OG somewhere around 1.050.
5 days is not a very long fermentation, especially when you figure your lag time (time between adding yeast and fermentation actually starts) could have been as long as two days or more. Relax and let the yeast do it's thing for a while longer. Don't even open it up for a few days, maybe a whole week. A lot of us let our beer sit for 3 weeks before we even touch it. It took 5 days to go from 1.050 to 1.030, now it's got to get from 1.030 down to 1.014.