Hi Helena,
Obviously, starting your DD at 4am doesn't help matters as that's just more hours to get through without food but hopefully that won't happen every DD.
On my DDs I have two high protein, low carb shakes from Exante, which amount to 400 cals in total, and then 100 cals of semi skimmed milk in coffees throughout the day. I have one shake about 9am and then another about 7pm. Coffees, a Coke Zero and lots of water during the day. I do get hunger pangs but they pass. However, I haven't felt light headed. I don't think that veg soup has enough protein in it and you probably need this more on a DD as it does tend to fill you up for longer. I like using total meal replacement shakes on my DDs as I know I'm getting at least 2/3 of my vitamin and mineral RDAs from these and I also take a supplement. If you don't fancy shakes then try using more high protein but low cal foods like cottage cheese and eggs.