What do you think?

So, I just turned 38,last week, and have a 4 year old daughter. After the birth of my daughter, my hormones were so out of sync and I bf for almost 3 years, my period was so irregular I didn't keep track. About 3 weeks ago, I noticed being really tired, breasts extremely sore and becoming larger, and my pants started becoming tight. Before my daughter, I was a steady 112lbs, at 5'2" but pp I was around 100 lbs and having a hard time gaining. I was too thin. Anyway, I started thinking I may be pregnant, since I wasn't on any birth control. I took a test and sure enough I am. This was about 3 weeks ago, I really have no clue as to how far I could be because I cannot remember (anything) when my last period was. Withing the last week and a half, I have really "popped" and I can't hide it. My husband and I aren't telling anyone until my doctor appt on Monday. But it's getting extremely hard to hide and uncomfortable. Today especially I feel like my stomach grew overnight, and I'm kind of worried I'm farther along than I imagine. I'm thinking 12 weeks, but really have nothing to go on. I was going on my size, but like I said, this week it's like I added a trimester. What do you all think based on this picture?