I second the walk a bit jog a bit thing.. And even though I've been running for years, I still stop and walk a bit sometimes. There are days when my body - or mind- just doesn't have it, so I give myself permission to stop and walk a few paces. It sure seems to help, and I still get the miles in. It also helps when I'm not wanting to get out the door. I remind myself that if all else fails i can walk. I usually don't, but giving my mind that "out" seems to be all I need to get out the door.
BTW- When I first started running back in the early 90's that is how I started. Bursts of jogging in my walks.. And look at me now!
Oh- and when I started swimming... I could barely make a length of the pool! I remember thinking "I can do a MARATHON but I can't swim the length of the pool!!!"... It's all about using different muscles and such. Don't fret, you will get there. I have confidence
Denise