It's absolutely normal to loose fantacy inbetween active sexual life!
Sex is multi dimensional and multifactoral causes are responsible for loss of interest in sex like physical inactivity, performance anxiety, partner response, work pressure with simple session of anxiety releif he should be back on track, is he having any physical problems like weight issue, performance anxiety or any medicine he is taking ?
Next Steps
If possible one counseling session should sort it out if he is normal because sex is natural and Normal act there is hardly any reason to worry if it's changed
Health Tips
Nothing to worry but don't wait even further take one possible offline session to nearest good family doctor, as your age 28 meaning husband and you are just in the beginning of your sex life and you need to get rid of it ASAP.