low blood sugars

Hillary
So I've been having a lot of bad headaches recently. I'm 28 weeks. 
This morning I woke up completely feeling off. Light headed and dizzy. Nauseous. And a huge headache. 
I got ready like normal stopped for breakfast. Ate at about 10:30, chicken biscuit from chic filet and a bottle of oj. Assuming if my sugar was low the oj would help me boost them. 
So I got to work and about 30 mins later I ate my yogurt and fruit with granola. 
Still felt horrible. Head pounding. Felt just Week and dizzy and I couldn't shake the feeling so I called my doc and they had me come in to make sure my blood pressure was ok. 
Blood pressure was perfect. But. My sugar was 53, so they were all like well that's exactly why you feel like this and gave me some food. 
But I had just eaten! Like not two hours before hand and I had felt like this all morning ?! 
How could my sugar be that low even though I had carbs and sugar ? 
It doesn't make any sense to me. My levels drop frequently. And I know the feeling very well. And I know when to eat something sugary to get them up again. Case and point yesterday I hadn't eaten all day and was out shopping and had a episode and started shaking and sweating and feeling like crap. So I shoved some chocolate in my mouth went and got food and I was happy go lucky. 
This was just way different then I've ever felt before. And my head is still killing me after they gave me meds for mybheafache. 
I am rambeling but I gues I'm asking how is it possible for my sugars to be so low after eating and drinking juice. 
And why would this one time be so different feeling then every other time I have low sugars ?( I've had it my hole life)