Almost half way

I can't believe we are almost half way through this pregnancy. It has been so long since I have been this pregnant that I had forgotten all the fun things.(Okay fun things with KK were hospital trips) You know like not being able to see my feet when I'm standing up, having a hard time sitting up on my own from the laying down position, and the best part, hardly being able to bend over to tie up my boots. Yeah, fun. I haven't posted a picture in awhile but I'll try and remember. I don't feel like I've gotten any bigger. And I got in trouble at the doctor's again because I lost weight again. I now weigh 13 pounds less than when I got pregnant. Apparently that's not good?...I feel like there is still plenty to go around. My doctor told me that if I was only 12 weeks he would have no problem with that but since I am in the second trimester it's a no no. He also said its not good that my heart rate is really low every time I go in there and that I should do something to elevate it a bit everyday....so I've lost too much weight, but be more active? What to do?