It could do with a pot if its own but the cessation of flowering isn't a sign of trouble. They don't flower perpetually. I'd start harvesting it and eating it. That will promote bushiness.

I'd repot in a container of its own, as floral suggested. These actually can grow to be large shrubs and with an appropriately sized root system :-) I'd also look into a faster draining, less peat-based, more mineral potting soil as well. These plants are quite happy in rather dry soil conditions and peat tends to hold too much water.

Thanks for the responses, I'll re pot it as soon as I get more soil!

I agree with gardengal's recommendations. It will be happiest in a big pot - 12" at the least.