I am so sorry for the pain you have - it's so good that you have posted here and that you are looking for help. I want to encourage you - that you know you are NOT alone. There are many resources out there - please visit this page:
Many Care Net centers offer FREE post-abortion counseling, and you should go.
Having another baby will NOT make your pain go away - and I think it's important that you find the healing you need before you attempt to have more children at this point. Your three children you do have need you whole and healthy - physically and emotionally and spiritually - all those pieces are critical in our lives.
You are welcome to email me, and talk more - please don't delay in finding the healing you need.