Climbing in Pakistan is much more difficult than in Nepal or India etc. There are few, if any, peaks considered to be 'trekking peaks' if by that you mean relatively low and easy ascent of peaks on snow and ice etc, like Island or Mera in Nepal.
The Naltar Valley, close to Gilgit, is relatively accessible, but the peaks are not necessarily easy and March is still right in winter. Further north it will be even more wintery. The only winter climbing I know of there was an ascent of an easy 6000m peak in Shimshal, but that is still a few days walk from the KKH, maybe more in winter.
If you only have a week, doing a decent size peak is out of the question, especially in March. You could maybe go walkign in the Murree Hills, or whatever that hill station place is outside of Islamabad, where locals go hiking.