Is it my imagination or do I have a lot more vaginal discharge now?

It's not your imagination. It's quite common to have more vaginal discharge during pregnancy.
What you're noticing is probably normal leukorrhea – the odorless or mild-smelling milky discharge that you may have noticed in your underwear before you were pregnant. There's just a lot more of it now, partly because of increased estrogen production and greater blood flow to the vaginal area. This discharge is made up of secretions from the cervix and vagina, old cells from the walls of the vagina, and normal bacterial flora from the vagina.
 
Inside pregnancy: Labor and birth 
Contractions begin and the cervix gradually opens. See the stages of labor and watch a baby being born. 
You'll probably notice more vaginal discharge as you approach labor, although it's likely to look somewhat different from the flow you've become accustomed to.
In very early pregnancy, cervical secretions filled your cervical canal and created a protective barrier – the so-called mucus plug. As your cervix begins to efface (thin out) and dilate (open up), it may expel this mucus, and you'll notice discharge that looks like egg white or mucus from a runny nose on a cold day. You may even expel the plug in one gelatinous glob. This discharge might be tinged with a bit of blood.

When should I call my caregiver?

If there's a lot of thin, clear discharge, it can be hard for you to tell if it's just mucus or if you're leaking amniotic fluid. If you have any doubt, contact your midwife or doctor.
Call your practitioner right away if you're not yet at 37 weeks and you notice an increase in discharge or a change in the type of discharge (if it becomes watery, mucus-like, or bloody – even if it's just tinged with pink or brownish old blood). This can be a sign of preterm labor.
You should also call your caregiver if you suspect that you have an infection. If you have an odorless, whitish discharge that's causing you discomfort such as pain with urination or intercourse, soreness, itching, or burning – or your vulva looks inflamed – you might have a yeast infection.
If you notice a thin white or gray discharge with a fishy smell after sex (when the discharge mixes with semen), you may have a different kind of vaginal infection called bacterial vaginosis.
If your discharge is yellow or green and frothy with an unpleasant odor, you may have trichomoniasis, a common sexually transmitted infection. Other possible symptoms of trichomoniasis (or trich) include a red, irritated, or itchy vulva or vagina and discomfort while urinating or during intercourse.
If your discharge is foul-smelling or frothy or yellow, green, or gray, you might have a different kind of vaginal infection or a sexually transmitted infection, even if you don't have symptoms of irritation, itching, or burning.
In any case, if you think you have an infection, don't try to treat yourself with over-the-counter medications. The symptoms aren't always easy to distinguish, so it's important to first see your practitioner for a diagnosis to make sure you get appropriate treatment.

Is there anything I can do about all this discharge?

If the discharge is not due to an infection, there's nothing you can do to stop the flow, but you can use panty liners to absorb it if you need to. (Don't use tampons during pregnancy.)
To keep your genital area healthy, keep it clean, always wipe from front to back, and wear cotton underwear. Avoid tight pants, nylons, bubble bath, scented pads or toilet paper, feminine hygiene sprays, and scented or deodorant soaps.
And don't douche – douching can upset the normal balance of vaginal flora and increase your risk of a vaginal infection. What's more, doctors and midwives discourage douching during pregnancy because in rare cases it can introduce air into your circulatory system through the vagina, which can cause serious complications.