wediblino, do eliminate medical causes. Just wanted to say that this is quite a tumultous age for a baby - loads of things happening in their life, like teething, starting to crawl/walk, starting to take more solids, separation anxiety. Combine that with a less laid back personality, and everything goes to pot.
The clinginess could be due to his being about to hit developmental milestones. He is thrilled and scared at the same time. Also, he has just realised that with his increasing mobility, he can move away from you and lose you . That is why separation anxiety starts. He is beginning to realise about the big world - exciting yet frightening.
I know what you mean about not trying cc because you are convinced it won't work. It is your mother's instinct about your ds' nature. I see how strongly my dd and ds protested everything and how worked up they got, it is no wonder they are probably not a good candidate for cc, at this age.
Please don't feel like a failure. Trust me, your ds may not be the most convenient at this stage, but this "anxiety" will translate into persistence, strong mindedness, sociability and liveliness, when he is older.
My dd is still bl__dyminded at 3.8, but she is also funny, a sheer delight - gives (and demands, lol) cuddles like you would not believe it. Some mothers long for this from their children. You are lucky, just have to get through the hard part.
The good news is that your ds2 will only get better - although it might get worse before it gets better. Toddlerhood will be a breeze, hth