your not alone
I think everyone's levels go a little bit crazy in pregnancy so don't panic. I used to get cross with mine and over-correct, making it worse.
My levels have been crazy, amknig me v. frustrated - here are a few things I've picked up in the last few weeks (13 weeks now):
PLACENTA AFFECTS IT
Apparently your placenta apparently 'mops up' some insulin, so in theory you're supposed to need increasingly higher doses of insulin as your baby grows and your placenta gets bigger. This is supposed to return to normal as soon as the placenta is passed after the birth. Or so my consultant told me. Any experienced Mums out there who can confirm whether this is actually what happens?
OTHER HORMONES AFFECT IT
Insulin isn't the only hormone at work here. You have 'counter-regulatory' hormones that protect you against hypos, so when you hypo, your body sometimes responds by creating a hypER which takes extra insulin to get rid of and can be annoyingly persistent. E.g. glucogon, which makes your liver release extra glycogen (which becomes sugar) into the blood.
Also, I think the sex hormones (you know, pregnancy hormones or whatever) mix this up a bit, too.
THESE AFFECTS DON'T SEEM TO BE CONSISTENT / ALL THE TIME
I had to increase my background insulin when I was first preg - I kept waking up with high levels and increased gradually from 14 to 24 iu. Then I started hypoing in the night and decreased my background dose again.
My fast-acting ratios don't seem to be consistent, either.
IN SUMMARY
It all gets really complicated and sometimes forces seem to be at work that you can't always explain, so don't beat yourself up. Phoebe's advice is excellent - don't get cross / stressed (easy to say, mind) and keep testing, testing, testing because your levels sure won't be as predictable as they used to be - and if you can't predict them, you need to test.
Work out the best correction doses for you, and always check again an hour later to be sure it helped