Hi Ashleigh,
I cannot add more than what Justin have already written in terms of a help desk app.
But since you are using Gmail to respond to your customer inquiries I thought you might also find our Storakle app useful in handling any support or sales cases as it will show you instant information related to your customer directly in Gmail.
The app is in beta now and is free so if you think it might be useful, do give it a try, we will very much appreciate it.