As others have said, he is at a tricky age and also sounds very anxious and needy. Definitely good advice to teach him to settle in/on a specific bed or mat and respond to the settle cue. He needs to develop coping strategies for being alone and this needs to be done very slowly and kept really positive, so that he gradually builds confidence. Basically, you need to keep him at a level just below his threshold for anxiety at all times and build up the separation in tiny, tiny increments. If you go over his threshold and trigger the anxiety, you'll need to go back a couple of steps to build his confidence back up.
Two useful books to read for understanding separation anxiety and how to treat it are:
Don't Leave Me, by Nicole Wilde. Which is an easy read and has good practical solutions and a programme to work with.
[[http://www.amazon.co.uk/Treating-Separation-Anxiety-Malena-Demartini-Price/dp/1617811432/ref=sr_1_1?s=books&ie=UTF8&qid=1427623071&sr=1-1&keywords=treating+separation+anxiety+in+dogs Treating Separation Anxiety in Dogs, by Malene Demartini-Price. Which is more indepth, as it was initially designed to help professionals work with SA cases, but is extremely useful for pet owners as well.
Anxious, clingy dogs are incredible intense to live with and it can and does get on top of you sometimes. I have a young Lurcher lad who was very similar at the same age. I've followed the advice in the books I've linked to and now, at almost 2 years old he's a different dog. He still doesn't like to be left for long, but he doesn't even lift his head when I go to the toilet or upstairs these days, whereas at 8 months he would scream the place down as soon as I went out of sight. I also leave him twice a day for school runs, when he has a green feeder (spikey dog bowl) of kibble, plus a frozen kong to occupy him while I'm gone and he's fine. The longest he's been left is an hour, because that's at the top end of his threshold, but we've found he's happy to be left for longer in his car crate, which is useful on occasion (although only through the cooler months unfortunately).
I would also hold off neutering for a while, as it won't make him calmer or more relaxed and if you go ahead it will essentially remove some of the hormones he needs for confidence.
My boy was neutered at 18 months old and I was extremely worried about it, having been advised by two different behaviourists (one APBC, one independent) that it was a bad idea, but the rescue he came from gave me no choice at that point. As it turns out, it hasn't had a negative effect on his behaviour at home (although his behaviour towards other dogs is a different matter
) but I wouldn't have liked to get it done any earlier and if given the choice, I would have waited until he was fully mature (probably about 3 years for his breed and size) or preferably kept him entire.
Other things to try, that may or may not help (all of them work on some, but not all dogs) are:
You can also try some Rescue Remedy (buy at Boots or Tesco) either dropped into in his water bowl or dripped straight into his mouth just before stressful situations.
The most important tools in your toolbox are going to be patience and empathy though. It's hard, I know from experience, but it really does help to keep reminding yourself that they are not just being a pain, they are genuinely really anxious and stressed.
As for him pulling at your clothes, sitting on you and generally being demanding. This comes under the category or self/impulse control and can be remedied fairly easily by just making it far more rewarding for him to do the opposite. The more self-control exercises you do with him the better his general level of self-control will become and this will help with his SA treatment as well. There are some ideas here, here and here but also things as simple as him having to sit and wait before being released through a doorway, sitting and waiting nicely for his dinner or treats, leave-it and wait can have a big effect.
It will get better if you get stuck in and do the work now. I went through a phase of thinking I would never be able to go upstairs in peace again, but now I actually smile when I come back downstairs and there he is still snoozing in his bed. It's slow progress and quite labour intensive in the early stages, but once you reach a certain point it's as if something suddenly clicks and they make rapid progress after that.