Can i fall pregnant 3 and a half weeks after giving birth / i havnt had a period yet i am still slightly bleeding after i gave bith not much tho ?

Very unlikely but: Ovulation and fertility tend to return 6 to 10 weeks after a term pregnancy is delivered and even later if you are breastfeeding around the clock. Pregnancy 3 and a half week after giving birth would be very unusual and quite unlikely. Be safe though; use an effective method of pregnancy prevention like an IUD, a subdermal implant or injections of Depo-Provera.

Sure: If you ovulated and had sex then pregnancy is certainly possible. Usually we advise patients to avoid intercourse until there post part visit where we discuss their birth control options.