In general, I would avoid giving my lo mineral oil. You can try flax seed oil instead. Also, make sure that your lo is drinking enough water. A lot of constipation can be fixed by upping the water intake.
When my dd is constipated, I give her magnesium. I know many mothers here like baby calm http://www.vitacost.com/Peter-Gillha...F-183405000032
Magnesium is great because it rehydrates the small intestine (not exactly sure if this is 100% the most accurate medical description...).
You might consider checking into food intolerances. Gluten products plugs my dd up (and dairy does in large does too).
Lastly, I swear by probiotics to help digestion issues. You can start with a supplement and also try probiotic foods as well.
Below are some general discussions about constipation that might be helpful:http://www.mothering.com/discussions...t=constipationhttp://www.mothering.com/discussions...t=constipationhttp://www.mothering.com/discussions...t=constipation