Curdled spit up?

My little one has had reflux since he was born, so he's always spit up, either very mild or almost an entire bottle. I brought it up to his pediatrician about 2 weeks ago, and he said as long as he's not losing weight, it's nothing to worry about. At that time his spit up looked just like the milk.

Now, at almost 5 weeks old, after changing his formula from Enfamil Infant to Similac Sensitive, and switching to Dr. Browns bottles, he's not spitting up after every feeding, and not nearly as much, but the spit up is curdled, and chunky, & seems to be mixed with a ton of saliva.

We have an appointment on Wednesday, but I wanted to see if any other mamas have had this issue, or if it's normal?