Dog with small lump

Hi there I have a 7 year old dashound / chihuahua mix she has this small lump under her stomach she's had it for about a few months now shes been acting normal so I don't know if I should be worried it's a very small lump but it is hard to the touch

Hello!  - and thank you for attaching the pictures.  I think I can see the lump that you mean.  It's important to check out, because mammary (breast) cancer and skin cancer may be differentials.  A lack of pain doesn't rule out cancer; indeed, cancer is usually painless at the time of diagnosis.  It is rare for vets to be able to identify lumps without taking samples or biopsies, so a single appointment may not give all the answers.  You can read more by running a search for 'lumps' or 'skin lumps' in the blog.  Wishing you both a good outcome to this story.