Low placenta

I’m 18 weeks and having terrible abdominal pains. Assuming it’s because of constipation or bloating or gas. Got worried and went to nearest TMC to check if baby is okay. Fortunately, baby is but that costed me $300. Ugh. Also, the doc mentioned my placenta is abit low. Do I need to be worried? I looked it up on google and some articles mentioned placenta praevia. Some mentioned once it reaches 3rd tri, the uterus will expand more and placenta would likely go higher.