howdy, emily--
i'd second the advice, above, that you take a good look at your strap and how you have it adjusted before you conclude you need a lighter instrument--unless your bass is a lot heavier than (say) ten pounds. IME a lot of neck and shoulder discomfort can be remedied with some adjustment in how the bass sits on your body and the biomechanics of both arms and hands as you play it. and trying a different strap is cheaper than buying a different bass.
for instance, if your strap is too long you might be scrunching up your left shoulder (assuming you play right-handed) to hold it up to where your fretting hand is comfortable and agile on the neck. or if you're using a narrow cloth strap suitable for a guitarist, you might benefit from a wider padded strap.
might be worth standing in front of a mirror and playing your bass, and taking a look for places you're holding some tension. ideally, the bass will kinda "float" in front of your body while both your hands "dance" on it.