Hi NaeNae
Sleeping for 7-8 hours does happen and is nothing to be concerned about.
Smelly yellow urine can be a sign of infection, dehydration or caused by some medications including vitamins. In your case, because the yellow smelly urine only happens occasionally I would suggest that it is related to either your vitamins or perhaps mild dehydration. What I suggest that you do is try to remember when you last had your vitamins. Did you take them within 48 hours of the yellow urine? You could also take note of how many wet nappies you get. I would expect at least 6 in 24 hours. In this case it is very unlikely that your baby is dehydrated. One last possible cause that I can think of is not passing urine foe a number of hours (sleeping for 8 hours). The small could be caused by the urine sitting in the bladder for so long and the yellow would be caused by no fluid intake for 8 hours causing the urine to become a little concentrated.