Please advise if it's ok to take vitamin b complex plus iron in a young adult like me?

Check levels: In two years you will be 40. Most people require a suppliment of d3 after age 40. B12 is often a problem but is replaced with a shot or a sub lingual form of the vitamin. Iron needs to be monitored with a blood tests. In short you can overdose on iron, vit b6, vit a, vit k, vit d, and vit e. Too much Niacin can cause liver problems. Ask your doctor's advice and to test your vit d and b12.