sounds not uncommon to me for babes to suffer after jabs for a few days. Don't be afraid to use calpol, as he may just be trying to tell you he does not feel well, but cannot express it and breast feeding is probably very comforting - the same way a toddler who is unwell will want to cuddle their blankie.
Don't panic about loss of routine. Go with what you need to do, and get back to your routine in a few days time. They do go back into their routine quite quickly at that age (it gets worse when they are older!!)
I do remember feeling desperate to stick to my routine, but actually it can be detrimental and stressful to both you and the baby. They will go back to it.
It's possible he's actually got something else wrong - it's normal for babies to have between 14 and 20 colds in their first year and low level infections often present as fussiness and wanting nursing all the time. I feel for you - I have a 21 month old and a six week old both of who are feeling crappy and want to nurse constantly.
Do give him Calpol/Neurofen if he's old enough - no point in either of you suffering unnecessarily!
It should pass within another three days, even post vax problems don't last further than ten days!
I would go to the dr and get him checked out just to be on the safe side. It will put your mind at ease. I am sure you will get your routine back. DD went into her her cotbed 2 wks ago and she was all over the place. It is only in th elast 3 days that she is back in her routine.