First of all well done for what you have achieved so far!
I used to run a 25min 5km and then had a baby. She is now 16 months and I've been back running since she was about 4 or months old so lets say a year. It is only the last few weeks that I have managed to run 5km in just under 30 mins so please please please do not feel disheartened. Trust me that 30min 5km is a major milestone and you will get there eventually, it's just best to do it without any injury on the way! I might suggest doing your warm up, then 30 mins of running and then run/walking up to 5km to start with increasing the run sections until you run the whole 5km. Once you have got to 5km your speed will increase over time.
I usually just go to Sports Direct to the He RUns She Runs department. I know a lot of people hate them but they are cheap! Even though I'm a bit bigger I wear lycra shorts mainly because they don't ever ride up thus preventing any leg rubbing issues... Mens t-shirts tend to be a looser fit and can be more confortable too.
I've using my swimming mp3 player and the earphones it came with and it's the best combination I've found for running as well as swimming. As it's completely waterproof and has a clip built in it's perfect and the earphones never fall out which has been major issue for me in the past. Check out Speedo Aquabeat 2.
Your body is telling you to give the running a rest for a reason, as horrible as it is to accept this (queue lots of hormonal crying...) it's best to listen. Just because you may decide to stop running doesn't mean you have to stop exercising take the opportunity to improve your swimming for instance by getting some professional lessons to improve your technique and set yourself a different goal. Every body and every pregnancy is different it's best to keep fit in a manner which is comfortable for you at the end of the day you should enjoy your exercise and you don't want to do any lasting damage to either of you.
I'm with everyone else here, it sounds like awful and potentially dangerous advice! Carb load in the days leading up to it and have a good breakfast like porridge on the day, only use the supplements/food you have been training with. I would also suggest that most personal trainers are not experienced distance runners (neither am I, only done 1 marathon and a couple of halves, but I listen to those who are!) and therefore don't necessarily have the most up to date information about our sport. I'm with RunningMax and avoid caffeine on long runs/training sessions as it just seems like "fake energy" to me.