2 year old bedtime routine changed

for last few months my 2 year olds betime rountine was good, he would be asleep by 7pm and would sleep through till at least 6am.
The routine i had was at 5:45 he would change into his pjs and have a beaker of milk, then at 6:20 i would take him upstairs to brush teeth and then spead half and hour sitting with him in the rocking chair reading him a book, then by 7 he would have fallen alseep.

However in last week he has started putting up a fuss when doing bedtime. He no longer wants to sit in the rocking chair with me he justs wants to run about or more books and then will get really upset when i wont give him any more books. Last night was horrible he refused to go anywhere near me, just cried and cried. Then by 7:20pm he had literly cried himself to sleep, it was so upsetting.

I don't understand what has happend, it was going really well at bedtime and now its so stressful and i can feel myself getting more more fustrated which i know is not going to help the situation.

Does anyone have any advice of what i can do?