So my world was created in 2013 but I have recently started playing it. I wanted to kill Queen Bee and Planterra, so I went to the jungle biome. I have mined all the way to the hell and from many sides but I am still unable to find either boss.
Queen Bee and Plantera were introduced in Update 1.2, which went live on September 30, 2013. If your world was created in 2013 before that date, the map simply didn't generate the Queen Bee area. However, to get Plantera to spawn, you need to kill all 3 Mechanical Bosses to make Plantera's Bulbs to appear at the Underground Jungle.
The best way to deal with the lack of Queen Bee is to create a new map, which will consider all the new information from new patches. You can use the same character on a new map to speed things up.
If you are afraid of missing the items, you can take them either inside your inventory, inside a Piggy Bank or the Safe. If you are playing the updated game, both of the items linked should have 40 slots.
All you have to do is place them, put the items inside them, then break and put them inside your inventory. Once in the new world, place them in the world and get the materials/items.
You have probably killed the mechanical bosses so I don't know why plantra isn't spawning just try leaving the game on while afk. However for queen bee create a new world get the stuff to make queen bee bring it to your og world and fight her so you can still get the witch doctor there.