Vitamin C is a Vitamin supplement for ur body. It boost immunity at some extent.
Vitamin C has no contraceptive effects.
Vitamins C when use as vitamin supplements, use orally. Never vaginally.
There are other effective methods of conception like,
1. Barrier contraception (Condoms)
2. Oral pills (Monthly Hormonal pills)
3. Injectable (Once a three month)
4. IUD (Intra uterine device like Copper T or Multiload)
5. Surgical (For permanent sterilization)
As per ur Obstetric history, either of these above methods shud be selected with proper Consultation and few blood tests, sonography.