Hi!
Can you please weigh your baby boar. If he is 250g or over and has been rumbling for several days, then he can potentially impregnate his mother when she comes into season for the second time around 15-17 days after giving birth. In this case or if in any doubt, you need to separate asap!
While impregnation during the nursing period by well developed baby boars is comparatively rare, it is by no means unknown. This is why we have introduced a weight qualifier into our own separation advice, seeing the vast difference in birth weights and size:
https://www.theguineapigforum.co.uk/threads/sexing-separating-baby-boars-and-rehoming-babies.109391/