What has your weather been like? And why do you want them out flying around? Do you have a strong nectar flow.
If I see a hive with minimal outside activity this time of year, I am happy as long as there is a growing colony inside the box. I want my bees to be spending their energy building up and raising brood and preparing for the main nectar flow, rather than to have the bees out flying around now wasting their energy searching for minimal nectar.
Do they have adequate food for raising brood? If not, give them a feeder with sugar syrup. Do they have plenty of pollen? If not, feed them some pollen patties. Even if you think they have enough pollen, given them a patty for good measure. Is your queen laying a nice pattern, and laying eggs in as many frames as the cluster can cover?
At this time of year, what is happening inside the box is much more important than activity you see outside the box.