I'd go see a doctor asap hun i was 6 weeks and was getting cramps that only lasted about 3 minutes it was horrible i thought i had an infection turns out i was 6 weeks gone im now 10 weeks and two days and still getting these pains now and again but everything is fine if you're a little skinny like myself you'll feel a little sore sometimes just due to the fact everything is stretching and preparing for the baby to bed down :) don't worry to much but go to you're doctor and get you're mind put at rest remember not to be stretching for things xx
I'm just saying I have been getting some stomach pain (cramping/stabbing pains) and my midwife told me it's due to the body having to prepare for a baby to be carried as there's obviously a lot going on inside us at the minute! And I was also told spotting is fairly common in the early stages. As your 4 weeks it could simply be implantation bleeding. But, it always worth going to the doctors to ask any questions/get checked out. Hope it all works out for you :)
Go see a doctor. There are multiple possibilities for you bleeding. It could be implantation bleeding, fryable cervix, miscarriage or even an infection. Miscarriage bleeding usually has blood clots like a period bleed though. So go see a doctor right away!