Is there a possibility that they can see my browsing history, media transfers, Skype sessions and even FaceTime?
Given that your IT staff are oblivious enough to allow to install your own WiFi access point, it's safe to assume they're not conducting advanced network analysis to figure out patterns in your encrypted Skype sessions or extract secrets from your HTTPS sessions.
Please note that the traffic is coming out of your laptop into the WiFi access point which is connected to your Office's router and then to the internet. The inbound traffic is coming from the Internet to your Office's router which will pass it to your access point and finally to your laptop. Whatever you're browsing or doing online can be logged and observed by their router.
Luckily for you, FaceTime and Skype encrypt their traffic. As for your other "media transfer" activities, if they're not over HTTPS then assume your employer knows about them and act accordingly.