I'm finding it very hard to stay motivated to keep exercising.

I cycled 5 days a week for 3 weeks and I didn't notice any change in my mood.

I do an intense 30 minute work out on a stationary bike. I get my heart up to 140bpm and I'm definitely tired afterwards. I tried to go longer but I can just manage another 5 min because I don't yet have the stamina to go longer.

I thought of maybe making it easier by using a lower gear so that I could cycle longer but I don't see the point.

I think I should have noticed something after 3 weeks, right?