Very good advice from incywincybitofa, and TatterdemalionAspie.
Especially "this is an opportunity to find something else in life to 'know'. The welfare of a child is more important that your feeling of wanting one because you don't know what else to do with yourself and want to fill the hole that losing your children has left you with."
I am mum to a little boy we adopted aged 3 (he is 8 now). One day he will have the chance to meet his birth mum and dad and I will encourage him to do so, if he wishes.
I know you see your children twice a year, and I am not going to encourage you to 'get your kids back', unless it was 100% the right thing for them. However, it may be possible/appropriate for you to try and see them more often if this would be good for them.
What has happened in your life is truly heartbreaking for your children and for you, but I really think you need to delay any decisions to have further children. You have said you are young, you know you are fertile. So really there is little risk in waiting, but there is massive risk in rushing in.
Your health, you have said health issues, which children or a baby could make worse.
"Im currently in a slightly better position mentally than back then..." Only slightly better than when your children were removed is really not good enough for what you want to do but maybe one day you will be much better and will be able to do this.
I would really suggest you explore PAUSE and please be aware the poem on the first page is very poignant and sad, and may make you cry, it brought a tear to my eyes.
www.pause.org.uk/aboutpause
Please, please, keep talking and thinking, I hope you will get the future you desire. Many women lose their children in circumstances similar to yours and I am not judging you at all.