Ill be 30 weeks on Saturday and my son has been doing the same thing lately. Not days in a row but at least a day. I looked it up and theyre just having growth spurts. At 18 weeks though their bones are still so soft sometimes they'll be moving a lot and you can't feel it. Nothing to worry about mama :)
I was having sharp pains to. My doctor just told me that I was dehydrated & to drink a half gallon of water a day. But yea it's normal for them not to move for a couple days. I guess they just be being lazy.
I have gone through the same thing starting at about 18 weeks as well! It's scary but they are still so small they might be moving without you even knowing it! I was told they have lazy days maybe when they are going through a growth spurt! Mine would be lazy for sometimes 3 days in a row and then after the 3 days be a busy baby! Try not to worry as long as your not cramping or bleeding its normal
Sometimes they don't move much and then you can't feel the movements. If you don't have any cramps or bleeding you should be OK but you can always go to the doctor if you are concerned.