Try another pair of headphones. If you get the same result, go into the Windows (I'm assuming this is your OS) audio mixer and ensure that the balance on your channels is in the center. If they're not, center them and you'll indeed have more volume and will no longer be lopsided, but whether that gets you as loud as you want to be is another question.
If, however, all your pans/balances are centered (including the mixer settings in your audio player, if applicable), and you've ruled out the headphones as being the culprit by duplicating the effect on another pair, then you may consider that there's something wrong with the headphone jack on your laptop or a component of the audio hardware.
Before assuming that, go ahead and update the drivers for your audio card for grins and giggles. If you're still in the same boat, it may be time to think about getting a small USB external sound card (24bit). With these, you'll probably also solve any volume limitations you may have had by using just the onboard sound from your laptop, fully operational or not.
External sound cards aren't all that expensive, and you're probably going to be upgrading from your current situation irregardless of what you buy as an external sound card (although I would suggest paying what you can afford). The onboard cards of laptops, particularly the consumer-line laptops, aren't exactly notorious for putting top quality hardware into their products.
Let me know if this helps.
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