freaking myself out

I'm 20 weeks, and all day today I've felt EXTREMELY tired. I thought it was the heat first so I didn't think much about it. Then while I was cooking dinner I started feeling really light headed, and started shaking. I decided to drink some water, thinking I may have been a little dehydrated. I also had this weird feeling in my lower abdomen. Not really a pain or a pressure just weird, and this achey feeling in my vaginal area. I went to go sit down for a while and my lower back was hurting. I'm not bleeding, not cramping and not having any weird fluid and I've felt her move a few times in the same spots that I usually do. I've passed a good bit of gas and thought maybe that's what's causing the discomfort? I'm just trying not to freak myself out. I tend to do that over every little thing this pregnancy and I'm really trying to stop looking into things so much.