Hi Jade,
That sounds perfectly normal at your stage of pregnancy. That's around when I got lows too. As you said, the amount of insulin needed to keep post-meal spikes down can mean going low later. So I ate and had the necessary bolus to keep the spike down, but then tested my blood sugar at one hour and two hours after my meal and ate something if it seemed low or was going down. I had to do this quite a lot, but reading various things on the Internet, it seems this is very common.
Also, watch out for nighttime lows. I had quite a few of those and I found Lucozade was the best way to treat them. I keep a bottle by my bed.