As others have said, it takes time for the skin to recover… after all it took 9 months for it to stretch out so big, so it will take time for the skin to tighten and for the stretch marks to fade. If the skin had been stretched for a longer period of time, it would take proportionately longer to recover. Also, the younger you are, the more elasticity there is in your skin. Genetics also play a large part, so consider your close relatives, and whether any of them have stretch marks.
My baby is almost 18, and I gained significant weight since then, so I have stretch marks all over now. I am currently losing weight, and the skin is getting loose and starting to sag. I’ve been doing research, and it seems that there really isn’t much one can do other than optimal nutrition and hydration and exercise. There are some very expensive creams and dietary supplements that claim to help with stretch marks, elasticity, and cellulite, but I have not found any supportive clinical evidence that compels me to dole out the cash they want!
The consensus is that it can take as long as 2 years after achieving one’s goal weight for skin to retract to the tightest is will ever be. At that point, if one is still displeased with the appearance, plastic surgery is the only option. Again, genetics, age, and the length of time that the skin was stretched are the main factors in how well it will recover.
I just looked up BioOil and their “Clinical Trial” for stretch marks consisted of 20 women—that is nowhere near enough of a populations size to be considered clinically relevant (ask any of our resident scientists and physicians); and it says that 50% of those women (10) saw improvement in their stretch marks after 4 weeks. Ummmm… yeah. I bet they’d have seen that if they had been rubbing Cocoa Butter, Shea Butter, Baby Oil, Olive Oil, Vitamin E, or anything else on their body, too.