I just began oboe, and it doesn't really seem difficult. When I FIRST started, I didn't have any problems, but lately I've been noticing that I have problems with my low D and C wavering uncontrollably. I'm not really sure what I'm doing different to cause these problems--any advice would be very helpful!

How long have you been playing on your current reed? When reeds hit the end of their lifespan a sure sign is loss of range down below.

Break in a new reed and see if the problem goes away and then you'll know the cause.

If you find yourself stuck on a dying with no replacement you can do two things:
1. Pinch the sides in so that the reed opens up more. That will work for a very short time and also speed up the rate at which your reed deteriorates.

2. Use your lips. Your embouchure should be round with an Ohm shape even though you lips are folded over your teeth. By drawing the corners of your lips further inward you'll press the side of the reed in a harmless manner.

Oh, and no dimples.

(3.) Use a reed knife. If your reed it pretty well on its way out you can play with refining the tip and/or body of the reed and see how good you get at bringing back the dead.

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Corrections:
stuck on a dying reed

If your reed is pretty

Is there any way to make my reeds last longer? I soak them before playing and I'm really careful with them (almost paranoid), but they seem to deteriorate faster than I can afford.

That's the bad side about oboe reeds.

Other than finding a cheap reliable source ( http://www.nielsen-woodwinds.com/ ) there isn't much else you can do except...

Reed wire. Bassoonists use it and the only store bought oboe reed you'll see this stuff on are Rico reeds which really give them a bad rep. Goodtone guild makes nice handmade reeds with the wires. I usually take wires off goodtone reeds as I find I hurt myself too often, lol. (they do offer to make them without wires too)

Oboe reeds with wires look like this:
https://jonesdoublereed.com/images/52_large.jpg

The wires in place do nothing until you find your reed collapsing/closing on you. You can pull the wire a little bit up and it will support the reed opening and the reed will live for a much longer period.

The bad part is that your tone and/or pitch may be altered somewhat when you use the wire... or not. When you do use wire to open the reed it may require a little break in to get to a normal opening. It's still always good to have back up reeds.

Most oboists would suggest dealing with life and moving on to a new reed. It does suck when you're young and don't have the money for it.

You could learn to make reeds. It'll just be quite expensive in the beginning as you'll burn through materials and ruin many reeds before you get a good one.

There are videos and books abound on reed making abound. Check out http://www.charlesmusic.com & http://www.forrestsmusic.com as well as Nielsen's on what types of supplies and books are out there.

Also do check out http://www.oboeinsight.com , a wonderful oboe blog with handy dandy links to oboe reed makers and all sorts of goodies on the left panel.