It can take some practice and breast stimulations. Here is nhs info page on colostrum harvasting , i thought this can helpful. https://www.nth.nhs.uk/resources/colostrum-harvesting/
Why don’t you give yourself a day off or two? Give it a chance to build up as well as let the pain diminish. Also, try not to feel any pressure. It’s not the end of the world if you don’t make any and you still may be absolutely fine with feeding in the future
The early days after birth are important to your supply so Its good to learn some tips and come with some knolledge. Here is my blog with somd tips of skin to skin, hand expression, and more.. https://mylee.life/blogs/mylee-blog/breastfeeding-the-basics
What are you in pain with to be taking 60mg codeine? X
Sometimes I have better sessions than others! What helps the most is having a warm bath, really massaging each side and making sure I'm in the right mindset. If I'm feeling stressed or my mind is elsewhere I feel like I don't get as much! Try sitting in the babies room or looking at scan photos/listening to music etc. I can imagine if you are in pain that that isn't helping x I wouldn't worry too much though, anything you get will be a bonus and your supply will increase massively once placenta is delivered 💕