Too much vitamins & diet pills?

It it possible to take too much vitamins? Is it bad to mix with diet pills?

Before breakfast I took:
- Daily-One multivitamin for women
- Omega-3 fish oil 1200mg
- B-12 1000mcg

30 minutes before lunch I took an African mango diet pill.

Can this harm me at all? Anything I should be cautious of?