Why does it feel like she's sucking my life energy?

I got back with my gf, and we were sleeping together. She loves me and I make her happy. It's just when we touch bodies, or when i'm near her body, my body physically feels weaker. It feels like she's sucking my life energry to the last drop. It happened 3 months ago especially when I found out one of her ex was a old man and had a bigger . Is this all in my head, is it jealousy or is it some warning sign? Should I run or wait for it to go away? Why do I feel this way? I'm feeling depleted I think.