Hi there,
I am a first time mum, so not sure I can offer any advice or guidance, but I can certainly understand and encourage you 
I also have a 7 month old and she has slept pretty well right from the beginning. Who knows why! I have tried to ensure that we have a bedtime routine for her naps during the day eg. wrap her, put some soothing music on in background, dark room and then rock in chair until asleep and then into cot. I also have a night time routine that consists of nudy walk through the house (
), bath, music in room, dark room and she lays in bed with me to feed (this really calms her and she often falls asleep here) and then wrap and into bed. This is trial and error though and doesn't always work, but works most of the time, which is good enough for me!
She has also started solids a month ago and has had 3 teeth come through in the same month (yipee) and she has more teeth on the way, constantly teething and needing pain relief (I use teething tablets that are homeopathic blend, Bonjela straight on gums every 3hrs if need be and if absolutely necessary some baby panadol).
Are you breastfeeding or bottle feeding? Don't think this should make a difference just interested as I breastfeed.
My little one has been waking once or twice a night for the past month and I put that down to her growing and being hungry, teething – therefore pain and development eg she is also commando crawling everywhere, and I figure she doesn't want to sleep she wants to practice all her new moves 
In regard to the dummy issue, I have never used one, but my brother does with his little girl and they are still having trouble getting her to go to sleep without it and she is 3 next month! So, maybe getting rid of it earlier is much better than later, but I can't really offer advice on that as I know how hard it is when they cry and all you want to do is help them and comfort them 
So, make sure you have a bedtime routine for naps and night time. Also make sure night time is not too worked up, so only quiet music and quiet stories etc, nothing to get them going and excited right before bed.
If he is moving around a lot, maybe he has a sore belly or sore ears? Often they won't sleep if they have an ear infection (imagine laying down flat with sore ears!) and the same with the belly. Pump his legs and bicycle kick his legs and rub his belly for him and see if that helps. Also, prune juice mixed with water might help get rid of any belly pain…
The other thing is to make sure he is not too cold or too warm (hard I know!), but that can also make him wake as he will be uncomfortable.
Is he very active during the day? Are you active at all? eg walks, shopping centres, floor time on tummy and back. The more you can do with him during the day, the more exhausted he will be at night and this may help him to sleep longer periods.
Anyway, long reply and maybe not that useful, but there could be one small thing in there that might help you. I really feel for you and hope that it does get better.
Cheers