Depriving Me of a Loving Relationship with my only Grandchild

I'm 72 and have been dealing with migraines for probably 35 years. When my grandson was born 12 years ago, I was having migraines almost every day which kept me home in bed. My grandson's father, my son, does not believe they affect me like they have and still do. I missed most of my grandson's growing up stage and so we don't have a close relationship which is so hurtful to me. I think my son resents me for this absence in his only child's life. I have guilt, and more guilt!!!