Hello Jojo,
Congrats on your twins! I am 29 weeks pregnant with twins and I had absolutely no morning sickness. I was very fortunate, just like some of these other moms and moms-to-be. But, I do have to admit, I was concerned as well at first but then quickly told myself to be happy about it.
Every woman is different. If you are eating well, feeling healthy and your dr. appointments are good - you are doing great.
I also made it a point to eat a high fiber cereal with lots of milk every morning and the recommended amounts of water (sometimes more) and have to say I have had no constipation either. Maybe one or two days... but in 29 weeks, I feel like the combo saved me. Such pleasant things we get to talk about as prgnant ladies!

and with having twins, I had no swelling until lately. I think the water helped with that too. But, once these little buggers get big enough, I don't think your body can help but get some swelling.
There are so many fun pregnant symptoms to choose from... One midwife told me "If you are having twins you can expect everything to be doubled... if you have morning sickness, it will be bad, if you don't get it in the beginning, you won't have it... if you get hemmoroids, you will get them doubly as bad, you either get a symptom two-fold, or you won't get the symptom at all." I don't know how much truth there is to this, but it did make me think about the morning sickness.