Plus sized and 40 - Fitness Help

I realize this may not be something many can answer, but I'm determined to get through this pregnancy as healthy as I can. If you have advice I'm all ears.

I work in an office and lead a mostly sedentary lifestyle. The two children I have are mostly grown and I'm not running after them so much. Seems like I'm aways sitting.

I used to be so athletic. Then I began to suffer with chronic back pain and I stopped moving. The pounds crept on...and on. Before I got pregnant I found keto. The next step was exercise.

But I'm newly 40, pregnant and due in April with no real idea what to do for fitness.

I tried my old warm up video for walking, just one mile - compared to what I used to do at the gym these are a cake walk...or so I thought.

I got about 11 minutes in and felt my heart start palpitating. I'm used to this when I'm not pregnant, they feel like skips, I've had them since I hit puberty. It's actually the heart adding extra beats and it can be a bit scary. But, as I said, I'm used to it and there's nothing a doctor can do for it.

I figured my heart was trying too hard to keep up and slowed my pace and got some water. It immediately calmed down.

Now I'm scared to move even more.

But I know I've got to. It helps so much with pain management. I already do physical therapy and massages.

Ladies, anyone out there older and above 250 lbs that can give me some guidance? I'm on BP meds as a precaution and aspirin cause I'm old and fat with a clotting disorder, but I want to do more without hurting myself or the baby.

Should I have taken it even slower? I've got my fitbit on and I'm tracking, my goal is to get to 7,500 steps a day in two weeks. Its hard though when I'm always in a chair at work or sitting in three hours of traffic a day. I need to move more without putting too much strain on my heart.

I'm aware there's extra blood flow now and that it's going to be a challenge.

Any help you can offer is appreciated.