As mentioned, sounds like you're doing the right sort of things, Pen and strep is a good general antibiotic that if he has caught a touch of pneumonia or any other bugs, a 3 day course of this should help fight that off. Liquid life aid is excellent stuff, really keeps them well hydrated and replaces a lot of electrolytes. It will be helping if he seems a bit dehydrated, and could help soften any slightly constipated faeces. Bloating is not great, and it is important to keep relieving the bloat, as this can kill if left. It may be worth getting some rumen powder, some liquid that helps with bloat, or some buscopan from your vet (this is a muscle relaxant that works on the guts, regularly advertised on TV for people now, which can help with crampy guts, constipation, bloating and general abdominal discomfort). As mentioned, probiotics are great, either regular live yoghurt, or there are some in the rumen powders, which also carry nutrients and vitamins, similar to the life aid, but a little more substance to them. I would also take it easy on the concentrates, as these can contribute to harder droppings and bloat, but hay and roughage are best for trying to get things back to normal. It isn't uncommon for artificially reared calves and lambs to get a bit of digestive upset and bloat when weaned, so this may be a part of it. Sounds like a bit of TLC and the treatments you have at the moment, plus some form of probiotic, +/- vitamin +/or buscopan injections from your vet may help. Also would be worth checking his temperature if he's shaking, may just be a sore gut, or it could be a fever, and alongside the antibiotic your vet may think an anti-inflammatory may help to bring down the temperature.
Hope he feels better soon
Suzanne