Pseudo-pregancy advice needed

My girl is 13 months old, and finished her first heat 6 weeks ago.

Her behaviour over the last week has completely changed and honestly its becoming quite difficult to handle so any advice or reassurance would be appreciated.

New behaviours include:

• Constantly looking frustrated and irritated, like she doesn't know what to do with herself.
• Being a lot more vocal. Barking, whining, or fake barking at either us or things that she wants. She even had a tantrum the other day and did a weird bark/moan and stormed off into another room lol.
• Refusing her kibble but eating treats
• No focus on walks. Suddenly stopping to sniff, or fixating on random people or things.
• Off-lead manners down the drain

I could go on but it's like someone replaced our lovely girl with a stroppy teen.

Anyone else had this? Please tell me it gets better soon...