Hello..are you me? (right down to the thumb sucking...which i still do at aged 41
)
This is exactly how i am and i too hate it.
With a huge amount of effort i do try, and it is a very concious effort.
We have games like "Guess who", card games, jenga that dont particularly require any imagination, but that means i can play with my child for 20 mins/half an hour.
Also and really importantly, i read to him every night at bedtime, this is good quality time, me & him.
After that, i tell him 5 things that has made me smile about him & really proud of him that day. I refuse to undermine his confidence because of the way I am.
If i am honest, i have been guilty of being "removed" and "distant" from my son, not because i am depressed but because i am just not interested in kids. NOW that is a confession on a parenting board isnt it!! 
Im not proud, but thats the way i feel. I do my damndest to NOT show it to him.
Its not easy, but just keep the big picture in mind and consider how you may be affecting them in the long run, small things done now, will make huge differences now & later.
Dont beat yourself up, you are not alone x