What Causes Bubbling Up Of Saliva In Mouth Along With Burps In An Infant?

My baby is a month and a week old. Lately he has been fussy, and little saliva bubbles come out of mouth. He squeezes his body together..feet to the top of tummy, complains if sleeping. He also has been throwing up when burped..it comes out white and thick. We have changed his formula four times. He currently is on Soybee from Enfamil. Any ideas if he s adjusting to formula? Or what it can be? Please help.