Growth spurts

Katelyn • Expecting #2 in September
Anyone have growth spurts early in the third trimester? I've been putting on about a half pound a day for the past couple of days and I'm not eating any more food than usual. I'll be 29 weeks tomorrow and I'm sitting at about 18 pounds in weight gain (If I don't gain a pound overnight). 
I am very sedentary because I have a desk job (at home) so I'm going to try and add in some yoga and light walking. I'm just a little alarmed at the rapid weight gain. I have a blood pressure monitor at home and if anything it's low and I'm not swelling, so I think it's actual weight!
What's going on!?