I keep smelling the smell of baby spit up at first i thought i was crazy but other pregnant woman on my app says its happened to them to why is this?

Hypersensitive, not: crazy. As Soul↔Mind↔Brain↔Body creatures, we routinely become super-sensitive to specific cues, depending on our situations & priorities. Recognition & memory of patterns is internal. Internal recall/replay of emotionally relevant patterns, including smells, etc., can be more vivid than actual recurrences of the same stimuli, which some (just by suggestion in dream like states) have experienced.

Heightened smell: Pregnant women often report their sense of smell goes into overdrive. I am not sure why you notice that particular odor but it is very common to report abnormal smells.