I don't feel the spark anymore

I've been in a relationship for 2 years now, Male (17) and Female(18), and I don't feel the spark anymore. That excitement when I'm driving to see her and I don't get butterflies in my stomach when she compliments me like I used to. The thing is, she's like madly in love with me. She's always texting ready to have a full blown conversation, she always tells me how much she misses me and how much she loves me, and she always puts in her utmost effort to be the best girlfriend. It's not that she's not enough, I also don't hate her but I don't feel very INTO her as she does for me. I don't want to seem like a dick or something but, she's not my type anymore you could say. She used to weigh around 120, but slowly she's began to gain weight, she's gained up to 50 pounds in the time we've been together. Now I know I'm not much to look at either but that's the thing, we don't look like we would be together, she's shorter than me but weighs more than me, when we first got together I would always like picking her up and carrying her just for fun, but now I can't. We have some mutual friends who are also in a relationship, we've gone out here and there on double dates and I always see him pick her up and I just feel, jealous? I've talked to her about it before the best I could, I told her I could go to the gym with her or something to better myself as well, she went one time and never turned back, she also shut down on me for like a week but I tried being as nice about it as possible but you know, I get it. She's one of those girls that wears sort of revealing clothes I guess but yk nothing too crazy, I always see her pull her shirt down so "nobody sees" but she does nothing to get rid of it. Today I took her to a flat area with dirt paths just to walk around and talk, but she got tired in 10 minutes and we ended up going home while I barely felt anything. Am I in the wrong at all for thinking this about her? And can anybody give me some advice on what to do or what to say to her?

**TL;DR;** : 2 Year relationship, I dont feel the spark while shes madly in love with me please send advice.