pls help and give me some advice

me and my partner have been TTC for around 8 years and never once have I been pregnant :( we have had all the tests done and it has come back as unexplained infertility, we have also had 2 filed IUI. the fertility clinic says it's best to go for IVF but I have to get my BMI down to 35 or under. I've had a weight problem all my life and I find it very hard to lose weight but I've been trying and for some reason I've lost all motivation as I can't deal with the heartache anymore.