Baby NOT gassy? Constipated?

I hope this isn’t a stupid question- but I wanted to see if anyone has experienced the same. My girl is a little over 4 months. She was EBF until about 3 1/2 months and then I transitioned to formula (similac pro sensitive). She’s always been a very gassy baby since day 1, never seemed to bother her. So I was concerned when I transitioned that her belly would be upset or that she may have extra gas or what not so I would add gas drops every couple bottles. It’s been a few weeks now and I swear she’s not near as gassy as she was when EBF and I haven’t even been adding the gas drops here the last few days as often. Maybe it’s a combination of her gut maturing and also the formula? But I realized this morning that I haven’t heard her pass much gas at all lately. I’m sure it’s a good thing but is this ok?? As far as pooping, she only goes every 3-4 days and it’s usually soft. That’s normal for her. But it’s been about 3 days currently that she’s went and I’m afraid she’s going to be constipated. Should I be proactive and go buy something for her now or wait and see? Maybe Im just over worrying? I’ve never had to give her anything yet for that. She’s also never had any solids, just formula.