hi mama, Iknow what you're going through.
My prepregnancy weight with dd was 263 and I'm 5'4". When I found out I was pregnant I had all the same fears you do. I made sure I ate REALLY healthy, lots of whole grains, legumes, fruit,and veggies and I didn't eat crap(until about the end when I got sick of being pg). I initially lost some weight (like10pounds) which my doctor didn't like, but I switched to amidwife who said as long as I was eating well, she didn't care what the scale said. Overweight women are equally capeable of having a normal birth. I continued eating well. I then gained about 15 pounds (put me at about 270) and then I had MAJOR swelling that put me at 280 (yikes!) and then after my baby was born, I weighed myself a week later and I weighed 255...8 pounds less than my prepregnancy weight.
I remember people commenting "oh, your not even showing yet!" and I was like 37 weeks pregnant and it bothered me a lot. I went in for induction and the nurse who came in to get me to get an ultrasound literally looked around the room for the pregnant lady.
All i can say is, every woman is beautiful when they are pregnant no matter what size they are and you will no doubt glow like the best of them! This is about you and your baby and that you two are healthy and happy....It's NOT about what others think. If it helps, I looked pregnant naked in the mirror, so you can probably strip down and you will see you're very pregnant self! Also, I didn't buy any plus size maternity and I think if you do, you will probably look more pregnant than if you wear regular clothes that are bigger.
I would nix the running if you just started it and just walk. What's important is that you are strong in the legs to help support yourself in comfortable positions when you birth your baby, NOT that you lose weight. Walking will be better for both of you. Also, if you want, go to the gym and tell them you are pregnant and need a specialized program,you will definitely lose some fat and gain some muscle healthfully and without harming you or baby. I would steer clear of the scale. Let them weigh you if need be and just avert your eyes and say you don't want to know or bye-pass it all together. Tell them you don't need to be weighed because you know you are eating healthy.
good luck mama, happy pregnancy!