Husband really hurting my feelings :(

So the first day of my last period was febuary 12, 2016. I was suposed to get my bc pills Jan 16th but my kids had rsv and got me sick and I was afraid to go into the office with all the pregnant women and babies. My second appointment I got snowed in and couldn't make it out of the drive way for days. From November until the second week of febuary my husband was working out of town from Sunday through Thursday night/Friday morning when he got home. Sometimes he was out 2 or 3 weeks at a time. When we went to the doctor they told us I conceived around January 27th. I'm pretty sure my husband came in the 28th or 29th of that week after being gone for 2 weeks and went back out for 2 more one week trips before he got a job at home. He's convinced he was out of town but I know he wasn't because we celebrated Valentine's day a week early and he had only been gone a week that time but was expecting to be gone on Valentine's day. He refuses to listen to me and even though he says he knows the baby is his and he trusts me he keeps looking at the calendar and saying he was gone. He makes snide comments about me probably having someone over while he works third shift (I have a 1 and 2 year old and am pregnant) when does he think I sleep???? It's really starting to upset me and I've offered DNA because I've not looked at another man in the past 2 1/2 years! He's the one who wanted to keep the baby at first because I was set on adoption because of finances and just not wanting a 3rd baby. I was getting very excited for the baby and even happy but it's hard with the way he is acting. The doctor says it's accurate to 2 days and if I'm right then it was within 2 days and if my husband is right then the doctor is just wrong. Any advice? Anyone else have this problem?