Forcus on quality not quantity. You could take a multivitamin, but most on the market are of little good to you body as they are unable to be properly absorbed and utilized in your body. So I would recommend researching quality 'whole-food' vitamins. Don't buy them at Walmart.
I recommend Standard Process Vitamins. They are organic whole-food synergistic vitamins that have one of a kind properties to them; the best I have come across. And the best part is, they are affordable!
But because 99% of todays population is calcium defficent, I would recommend taking a good calcium supplement. But make sure you are aware that there are 2 seperate types of calcium: 1. that which goes directly to your bones and teeth, 2. that which is absorbed into the blood. For instance, calcium phosphate powder will go directly to your bones, calcium magnesium or some calcium lactate tablets go to your blood. Its best to consume a combination of the powder and tablets, as one with strengthen bone structure and the other regulate your PH level, which is important because a Ph of 7 or higher disallows carcinoma (cancer) cells to begin formation in the human body.
You should also take a multi-vitamin. Again, I would point you to the standard process multivitamin called 'Catalyn'.
It wouldn't hurt you to take a special vitamin complex such as Cataplex ACP,& D, and the B-Complex vitamins consisting of Cataplex G and Cataplex B.
If you have trouble digesting proteins, think about a good enzyme, and if you dont consume enough veggies, think about including a scoop of energy greens into a shake every day.
That should give you a great start.