I have heated up my empty pot gently, taken it off the heat and added the bees wax to it putting it back on a gentle heat if needed. you need to keep it hotish as when you add your cold oils the wax will set again, it is best to add the hardest oil first as that needs more heat. If it does start to set up you can reheat the lot best to do it quickly, mix till it is all mixed together and then add the rest of the oils according to the temperture required.
you need to make sure you have every little bit of that bees wax melted or it will just stay in lumps.
You can also heat your hardest oil in another pot and then add to the beeswax, best to add the hot oil to the bees wax not the bees wax to the oil.
Hope this helps