Sex life

I've been with my husband for 5 years now and my sex drive has been very low the past year (I did just have a baby 9 months ago) I feel bad and am afraid he's going to cheat on me ( even though I know he's definitely not that type of person), I think my biggest draw back is my self esteem, I've always been plus size but when I was pregnant my weight was at the highest it's ever been and that did not sit well with my mental health, I have a huge problem with staying motivated to work out and eat healthier but I want to better myself for him and our daughter, so how do I get motivated and get my sex drive up?