Obiwan, your baby sounds similar to how mine was. He was gaining weight, so medically not a big concern, but very uncomfortable with the arching back, not wanting to lie down etc. I went a little crazy with worry during that period. I actually consulted 5 different doctors in a 3 month period, in addition to posting on these forums, consulting other moms with reflux babies and getting breastfeeding advice.

Here's the good news. Most babies grow out of it by 3 months. The very first pediatrician I consulted told me this, and it turned out to be true. I can't remember exactly when, but at just around 3 months, my boy was suddenly better. Never been an issue since.

There is lots of advice and tips out there. What I tried and what worked for me:
1. Keeping the baby's mattress elevated so he's not lying down flat. I did this. Not sure it helped but I kept it up anyway. Actually, my baby liked to lie on his side... there might be some SIDS risk here but it was the only way he would sleep. We also used a pillow for him. You could try putting the pillow under the fitted sheet.
2. Breastfeeding from only one breast each time. It was suggested that a foremilk imbalance might be causing my son to be gassy. Reflux babies are often very gassy. I think this helped.
3. Using Dr. Brown's bottles. These have a special design to prevent babies from gulping too much air (again making them gassy). I think these really helped so if you're bottle-feeding try these.
4. Burping very gently. My baby was a bad burper... really hard to get a burp out of him. It was emphasised to me that I must burp him. Though I don't think burping made him feel any better.
5. Diet modification: This one drove me round the bend. I started out cutting out cow's milk, the most common culprit (if you're considering this it takes at least two weeks to get cow's milk out of your system and the baby's, and a range of things contain cow's milk including sausages!). Then I cut out eggs, nuts, and gradually almost everything until I was eating practically only congee and a few pieces of chicken. The good thing was that I lost a tonne of weight. The bad news was that I was miserable (imagine breastfeeding and eating only this) and my son was only marginally better. In retrospect, I don't think my own food had anything to do with it and I would never go that route again. The jury is out among doctors on whether diet has any effect (the 5 doctors I saw were almost evenly split on this) though some mum's swear it helps. I guess if you see a dramatic result by eliminating one thing then it makes sense.

My son wanted to be held all the time, and was a terrible napper. The moment you tried to put him down, he'd wake up and howl. I think this is common among reflux babies though I was so sleep deprived. Eventually, I went the medication route (Lansaprazole) and that seemed to help. But weirdly, after a while, it didn't seem so effective. Luckily, he grew out of it soon after.

Things I didn't do:
1. See an osteopath: Some here have suggested this and I would have given it a try except my husband was against it.
2. Switching to formula to rule out allergies: There are special formulas for reflux babies. Lactose-free formula, hypoallergenic and thickened formula. I actually have three tins of these, samples given to me by a doctor - I only opened the hypoallergenic one (Nan Ha) and then didn't even give it to my baby. At the time I was exclusively breastfeeding and didn't want to use formula. However, if you are already using formula and want to try the special one, I can give you the tins. The Enfamil Lactose Intolerance and the Enfamil thickened milk are unopened. PM me if you want them.