I run Ubuntu 12.04, and for some reason bash does not keep my command history. the ~/.bash_history file contains only 3 commands that I typed a few months ago.

How can I fix this?

EDIT:
here's the relevant content of my .bashrc:

# ~/.bashrc: executed by bash(1) for non-login shells.

# see /usr/share/doc/bash/examples/startup-files (in the package bash-doc)

# for examples



# If not running interactively, don't do anything

[ -z "$PS1" ] && return



# don't put duplicate lines or lines starting with space in the history.

# See bash(1) for more options

HISTCONTROL=ignoreboth



# append to the history file, don't overwrite it

shopt -s histappend



# for setting history length see HISTSIZE and HISTFILESIZE in bash(1)

HISTSIZE=1000

HISTFILESIZE=2000