Wow, that's very interesting. There are many possibilities about what's going on- from a self aspect that is actually protecting you (they're not always nice or sweet) to a 'true' dweller, who wants to prevent you, and other related things. Did this start happening when you consciously put out the intention to go to the past (that is, this one mission)? A few things come to mind, but first of all, I would do a little prayer and shielding and set out the intention to do what is in your best interest, and ask a guide or Higher Self (or guardian angel, whatever you believe in) to take you to where it's best for you to go, and then leave it up to them to decide. In the past I've had a similar problem (not in the form of a dweller, but in the form of barriers and confusion), and when I stopped trying to direct myself and asked for help I was taken exactly to where I wanted to be, so that's all I got as ideas go, (for now.)