SurrealLife saidWhere is MunchingZombie when you need him?
*swoops in* Here I am! And it looks like a lot of good advice has been given so far.
What kind of lube are you using? If it starts to hurt after 5-10 minutes your lube could be drying out. A good oil based lube like BoyButter
is great for solo play and is compatible with all toys (but I wouldn't use it with electro toys).
Have you tried using an inflatable plug? After you work yourself over with a smaller one, stick in an inflatable. It is a great way to work up from smaller to larger toys. But for the love of god, if it starts to burn or hurt deflate, pull out, and try again later. Never keep going even if it hurts. It is a great way to injure yourself and makes disease easier to spread.
Finally, poppers and numbing sprays or lubes might be fine when you are playing alone, but don't use them with someone else unless you have an experienced hole. You will just end up taking more than your butt can chew.