Flight traveling around 18-20 weeks

Flying out to visit families when I will be around 18-20 weeks. Doctor said it is perfectly fine to fly, but try to avoid the security walk through screening and just ask for a pat down instead. Pressure in air will not harm. Didn't say anything else to avoid or be careful of. This is my first time flying when pregnant. Any more advices or what else I should be aware of? Any experiences and is ok? Will only be a 3.6 hours flight and a long 6 hours drive to another family.