Hi,
I had an identical problem with my dd up until around 6 months. I constantly had the washing machine on as she was going through several sets of clothes a day and about 6 muslin squares!!!
My Health Visitor was never concerned because as with your little one my dd was putting weight on and it never seemed to bother her when she was bringing it back up.
They just put it down to the little flap of muscle part way down the oesophagus not being mature yet (which is the case with all babies I believe) - it's just that with some you get more of a problem with the milk coming back up.
My dd wasn't as big as your little one at 14 weeks but she was taking 7 fl oz per feed quite early on - although I can't remember exactly when. I think we both just have hungry babies who want more than their tummies can hold
I found that she just started to grow out of it especially once she started to sit on her own.
One thing I found helped a little bit was using Bfree bottles (formerly known as Dr Browns). You can get them from Boots or Mothercare from memory.
I think as long as your little one is happy and putting weight on I wouldn't worry about trying different formulas or baby gaviscon. It is a pain from the mess point of view but it will get better.
The above is just my experience and opinion - definitely see what your doctor has to say.
Good luck and I hope things improve for you soon