1) DO get the reflux test
2) No single formula is best for all ______ BUT there are often "magic" formulas for each baby!!!
My son was MUCH older when starting formula (I've also been around a LOT of infants, but more on them in a bit). As in 10 months. Most formulas made him varying degrees of violently ill. We had gas (screaming pain gas). We had projectile vomitting (fun). We had diahrreah. (There's a Dave Barry article about colonoscopies which about covers the descriptors there). We had constipation. It was soooooo trial and error. For *my son* (please note the stars), the formula had to had to had to be PREMIXED enfamil lipil. Very specific. Powdered made him as miserable as several of the completely 'wrong' formulas. How I eventually "found" that formula was ditching all powdered, period, and buying every single premixed formula out there. I came up with a short list of "not terrible" ones (ones that didn't cause projectile vomiting and diahreah). And from there tried each of my short list for a few days to a week. Most STILL gave him gas that had him miserable by night time.
The "worst" for us were the "gentle" or "antigas" formulas. They made him sick as a dog with... wait for it... gas and vomiting.
The only 2 that left me with a happy bambino were Nutrimigen & Enfamil Lipil premixed. Never could do powdered.
Does this mean that Enfamil Lipil is a wonder formula? Nope!!! That formula will cause gas, vomiting, and/or diahrhea in OTHER infants... the same way that OTHER formulas caused those lovely things in him.
It really is TRIAL AND ERROR. No way to short cut it.
Remember how I mentioned I've been around lots of infants? When there are digestive problems (gas, vomiting, diahrhea, reflux), changing out formulas is one of the most tried and true ways to nix them IF it's the formula's fault. (Sometimes there are other issues at play). Pick a brand and type, any brand and type, and I've seen that be "The One!" for a newborn-infant AND "Eeeeevil! Pure unadulturated eeeeeeevil!" for another one.
Trust your gut (no pun intended, promise) on what is and isn't working.
DO start with the stupid expensive premixed ones, though, since you're already having problems. They're silkier/creamier/thicker/oilier than powdered, and it negates 1 set of problems. Start off with premixed, find one (I hope) that works, THEN try the powdered version of it.
3) Reflux babies often aren't formula problems... but immature digestive systems / structure problems that are literally 'grown out of'. I've only had 2 reflux babies in my care... one had to have cereal mixed with her bottles to thicken it enough to stay down... the other NOTHING would keep things down. BOTH slept in carseats for a good 6mo to help while sleeping. There's probably a lot more in the way of tips/tricks... but again, I only have those 2 as comparisons.