Will i have problems getting pregnant having an ileostomy and being under weight?

Probably not: The main fertility problem women who are underweight have is that many will skip menstrual cycles or stop altogether. This is a fertility problem! if you have a normal regular cycle, it's unlikely you'll have problems regardless of your weight.

Depends: I think it would be useful to understand the entire medical background to everything going on. There could be scar tissue in your belly affecting fallopian tubes, and weight loss if extreme can affect ovulation.