Sneglen, To go from no running to 5 times a week is a big ask, and it may've been better to start with 3 and gradually increase the time on your feet. That said you have coped, and the fact that you are tired might be down to you running too fast. Certainly have an easy week, with maybe some light gym work, swimming etc. I seem to remember you saying that it was hard for you to stick at 70%? Maybe try and be a bit more focussed when you get back into training, and stick to 70% max. Just limit your running to 2 or 3 times this week, and make it as easy as you can.
Dprovan, A cold will elevate the HR as it is working a little harder anyway trying to fight of the virus and keep the temp down. A rule of thumb is if the cold is above the neck then it is ok to run easy, but if it is below then don't run. If your HRmax is 198, and you are wanting to build time on your feet, then I would aim to stick to 70% max which is ~140. Don't worry about the pace or miles whilst in this building phase, work on time and HR (70%) till you get up to 6-7 hours on your feet per week.