They sell all of those group of drugs in the pharmacy, some you will need a local prescription for (available from a primary health doctor or specialist) but usually just buy over the counter. You are required to carry a medical certificate or copy of prescription when entering Qatar in case you get checked but as long as you are just taking the medication for yourself and not trying to import it for others you will be ok. Receiving medications of any kind by post is an absolute no. It is illegal and anything medicinal will be kept by customs (including a face mask I ordered from Elemis but I did get it back.)