All you need are lots of Pidgey and a lucky egg. Low powered Pidgey are plentiful in most places and require only 12 candies to evolve into Pidgeotto, an act that normally gives you 500XP. With a lucky egg active, which doubles your XP for 30 minutes that becomes 1,000XP per evolution.
By collecting loads of them and evolving as many as possible in 30 minutes with a lucky egg you can set somewhere in the region of 30,000 to 40,000XP at full burn with a strong internet connection. At lower levels that’s enough to jump at least one, possibly two levels. After you’re done with all the Pidgey, just trade in the resulting Pidgeotto to start collecting candies to do it again.
I know catching Pidgey is not exciting at all, but if you really want to level up, you can try this tip. I’m sure you already did this, but maybe not in a very organized way.