My Husband started to get desperate!!

Hi everyone! We are married for about 4 and half years now and I am conceive with my 1 st baby and 7th month running now by God's grace. All these years of marriage life my Sex Drive was very high and he was not that high and was too much focused with work. But since last few months his Sex urge has increased a lot gets horny every now and then but I don't feel like. Please let me know why is it so and what is the solution. My husband does not force me though as he understands me that I am not feeling to do but I feel bad for that..