Rhogam shot

Anyone here kung anong best weeks ng pregnancy mag pashot ng Rhogam and kung saan makakahanap at magkano. ? Im a Rh negative I have my 1st baby she’s 2yrs old Wala akong idea sa Rh ko nung 1pregnancy ko nalaman ko nalang nung 2nd but nag miscarriage ako 6weeks palang and now I’m pregnant 5 weeks and 4 days based on lmp. Please enlighten me