It is early days yet. Actually they didn't used to let people do DAFNE for some time (6 months/1 year) after diagnosis because in the early months things can vary a lot (at diagnosis you may need a bit more insulin and then sometimes peoples needs drop off considerably for a while before increasing a but again) Thats one reason that your nurse is being conservative about how much insulin you take and how much she wants you to vary it by. If you vary too many things at once it really is difficult to work out what's causing what. The rise after your dinner suggests that you are correct and that 4 units would have been better but until you know how many carbs you are eating then it's hard to judge.
Carb counting is a very important skill to learn.
Jack has linked to two carbohydrate counting primers, there is also one from diabetes UK
https://shop.diabetes.org.uk/usr/downloads/Carbs-Count-2012-reduced.pdf
Personally, I would stick with learning to count carbs to start with (rather than trying to do too much dosing adjustment without the guidance of your nurse)
Get yourself some scales, a calculator, read labels and get a carb counting book or use a web based resource
(You have to be careful though with some of the web based sites as they are crowd sourced with people from all over the world , the US lists carbs slightly differently to the UK and unfortunately the input methods don't allow for this, also people vary in how accurate they are with their data entry )
Personally, I would use a good UK book. There are two that from reports seem to be good ( I use a French book as I'm based there)
1) Carbs and Cals this helps give a visual record of the carbs in foods at different portion sizes (you can google them they have a website)
2) The calorie, carb and fat Bible (this is a UK based book)
(
You will often find people suggesting the little Gem carb counting book It's small and good for carrying around but I have got that book and , I've seen some very odd carb counts . I won't add to the complications by trying to explain why I think that has happened !.)
This
site uses the C Cand fat bible and has quite a lot of free listings which can be useful.
I would keep very detailed records of what insulin you take, glucose levels before and two hours after meals (and on waking and going to bed)
What was in the meals and how many carbs the meal contained. When you exercised an it's result on glucose levels (test before during after and have some hypo treatment on hand)
It sounds a hassle and to be honest it does take time but you won't have to keep such detailed notes for ever. What you will learn is how your body reacts to different foods, exercise etc. You will be able to see patterns.