You need to take her to the doctor... this kind of symptom could be due to many reasons. Don't second guess it...
Remember, "spit up" is about less than a tablespoon of "stuff." Whereas, "vomiting" is a bigger volume...and because she is also "projectile" vomiting... this is NOT spitting-up. And since she is also expelling stuff "hours" after feedings... I would think that this is not traditional "spit-up."
I used to baby sit a child from the time she was 6 months old, until she was about 2.5 years old. This girl did the exact same thing your baby is doing. -- sure, the baby was not bothered by it, it didn't hurt her... and she didn't even seem to notice her throwing up. And yes, it sure is messy. And yes (in response to the other poster)... she WAS breastfed by Mommy since birth, AND had bottles of breastmilk for her when I baby-sat her. This made no difference in this child. She had vomiting problems since she was a newborn, as I learned afterward from the Parents.
However, since this was not normal to me...nor to my "Doctor" friends... I constantly told her Parents to take her to the doctor, as this is not normal per say. BUT the parents always just shrugged it off and said "that's just the way she is... each baby is different..." It was SO frustrating. HOWEVER, under my eyes... this baby was also not developing well... she was also, per her well-baby check-ups, at only the 10th-5th percentile in weight and growth... and as an infant she suffered from dehydration & twice had to be taken to the ER because of it (this is per her Parents)....and her development was delayed as well throughout the time span that I cared for her. Her vomiting never stopped or lessened or subsided. But yet, her parents never did anything about her vomiting.
In her case, I consulted many of my Doctor friends.. .they said it could be anything from allergies, to internal digestive problems, to reflux, to Pyloric Stenosis, to GERD, to gastrointestinal problems, to
the opening of the esophagus and how the muscles there may not be coordinated thus it does not go into the stomach... etc. But without examining the girl... no one can really say what the EXACT problem is. But, her parents never did anything anyway.
Well this is just one example and experience of mine. Your baby is only 5 weeks old... I would not give her anything or Enfamil, or formula, without consulting your Pediatrician first.
Sometimes, it can just be due to a newborn's immature digestive system still...thus they "spit-up." And as the body matures, it subsides. But check with your Doctor.
Here is a link on "projectile vomiting in newborns:
http://www.thelaboroflove.com/articles/infant-projectile-...
http://www.google.com/search?q=projectile+vomiting+in+new...
All the best and take care,
~Susan