Advice..

So my husband and I have been married for a year and about 4 months but we've been together for 4 years. We have two kids (10 months and 2) and our sex life has drastically went down hill... we have "us time" maybe once a month and it use to be 5 times a month.... just for the past 6 months it's been hard to even get him to get "in the mood".. he doesn't like lingrie, I've bought some sexy undies and new bras, I'm basically tried everything I can think of. I don't have anyone to talk to about this and I'm very insecure about asking strangers but I need help. I've been wondered if it because I'm the only person he has ever had sex with and is loosing interest of if its because im not as skinny as i use to be and i now have stretch marks. Im not has pretty as i use to be. I'm just so confused and really need help.