HCG (Human Chorion Gonadotropin) is a hormone that is produced by the throphoblastic cells during pregnancy, starting about the 10th day after conception. Detecting HCG (in the blood or urine) with pregnancy tests confirms the pregnancy. HCG stimulates the yellow body to produce the sex hormones (progesterone and estrogen) that are necessary for keeping a pregnancy. HCG also stimulates fetal gonads to produce sex hormones that are necessary for developing baby’s reproductive organs during intrauterine life.

HCG is very similar in chemical structure and function to Luteinisating Hormone (LH). LH is produced by the pituitary gland and stimulates the ovaries to produce estrogen (in women) and testicles to produce testosterone (in men).

For medical purposes, HCG is used for therapeutic treatment and diagnostic reasons. HCG is used for inducing ovulation in some cases of sterility together with a Follicle stimulating hormone (FSH) or a Human menopausal gonadotropin (HMG)-mixture of FSH and LH. For diagnostic purposes HCG is used to estimate the gonads' ability to produce sex hormones (estrogen or testosterone).

In your case, I don’t see the reason why you'd want to use HCG-injections. Birth control pills contain estrogen and progesterone. These hormones are not contraindicated when taking HCG. In fact, estrogen acts together with HCG for inducting ovulation. Progesterone is necessary after ovulation for preparing the uterus for implantation of the fertilized egg-cell.