I am also rather underweight and have been trying (rather unsuccessfully) to gain weight for months.
I know what you mean about the barrier. Mine is the fact that I hated my body for so long, got used to it, then found out I need to put on weight. And also the fact that my boyfriend really likes my figure (he wants me to put on weight, but I'm worried he won't find me attractive if I do).
One thing you need to consider is that not everyone needs to be the same weight. You need to take into account your BMI (google if unsure). Don't be pressurised by under-8-stone celebrities, as your height might mean you need to be a lot heavier than that.
With regards to anorexia, I'm not really sure what would constitute having this. Maybe if you are obsessed with food, plan meals beforehand, avoid certain foods.
Are you happy with the way you look at the minute? If you are, then this could be your barrier.
I don't really know if this has helped or what to say - as you said, you didn't know what you were expecting - but best of luck with your situation. xxxxx